Modem relay over packet based network

ABSTRACT

A method of performing a negotiation session on a modem connection. The method includes receiving a plurality of negotiation signals from the source modem, by a first gateway, forwarding at least some of the received negotiation signals from the first gateway to a second gateway, over a packet based network, receiving, by the first gateway, responses to the forwarded negotiation signals from the second gateway, forwarding the responses from the second gateway to the source modem, by the first gateway, and transmitting from the first gateway to the source modem, response signals to at least some of the received negotiation signals, without receiving a response to the at least some of the signals from the second gateway.

RELATED APPLICATIONS

The present application is a U.S. national application ofPCT/TL01/00455, filed on May 21, 2001. This application is also relatedto PCT application PCT/IL00/00288, filed on May 21, 2000,PCT/IL00/00492, filed on Aug. 13, 2000, PCT/IL00/00657, filed on Oct.17, 2000, the disclosures of all of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to communication systems and in particularto systems which utilize modems.

BACKGROUND OF THE INVENTION

Traditional telephone networks comprise switched networks, e.g., thepublic switching telephone network (PSTN) and ISDN lines, in which aphysical link path is established between the end users of a call. Thevoice signals of the call are passed, generally in a time domainmultiplexed (TDM) manner, on the physical link path. On the other hand,data networks, such as the Internet, are generally packet basednetworks.

Due to the wide availability of switched network lines, these lines arecommonly used to access packet based networks. Data connections passedon switched network lines are referred to as voice band modem (VBM)connections. At opposite ends of a VBM connection, modems translate datasignals into voice signals and translate voice signals from thetelephone network into data signals. The tasks of the modems aregenerally divided into a plurality of layers. From a top down view, afirst layer performs data compression (DC) tasks. In transmission, theDC layer receives data bits and provides compressed data bits. Inreception, the DC layer receives compressed data bits and providesuncompressed data bits. The compression is used to conserve bandwidthand is optional. The data compression is performed, for example, inaccordance with the V.44 or V.42bis ITU recommendation or the MNP5standard.

A second layer, referred to as an error correction (EC) layer, performstasks which are generally divided into two modules, a link accessprocedure for modem (LAPM) module, and a high level data link control(HDLC) module. In transmission, the tasks of the LAPM module receive astream of compressed bits (if compression is used), break the streaminto frames and add to each frame a type, sequence number and anacknowledgment field. In reception, the LAPM tasks acknowledge thereceipt of the frames and send the transmitting modem indications on theamount of unused space in the buffer of the receiving modem.

The tasks of the HDLC module, in transmission, add an error correctionfield (e.g., CRC) to the transmitted frames and pad the frame with flags(e.g., 0x7E bytes), according to the transmission rate of the modem,such that the number of bits transmitted in each time interval isconstant. In reception, the HDLC module removes padding flags and theerror correction field and discards frames with an erroneous CRC.

A third layer, referred to as a data pump (DP) layer, performsmodulation and demodulation, i.e., converts data bits into voice symbolsand vice versa.

Data transmitted on a VBM connection is generally handled in accordancewith the DC layer, EC layer and DP layer by the transmitting modem andby the DP layer, EC layer and DC layer by the receiving modem. Thus, thesame layers are applied at both end modems of the VBM connection,although the receiving modem substantially reverses the operations ofthe transmitting modem.

Although most modems perform the tasks of all three layers describedabove, the term modem covers apparatus which performs DP tasks even ifthe other tasks are not performed by the apparatus.

VBM connections may be established between client modems, which areconnected to a PSTN through twisted pairs, between server modems whichare connected directly to the infrastructure of the PSTN, or between aserver modem and a client modem. The various connections may beestablished in accordance with various standards, such as the V.22,V.32, V.34, V.90, V.91 and V.92 ITU recommendations.

In establishing a VBM connection, a pair of modems, on opposite ends ofthe line, perform a negotiation procedure in which the modems test theline and determine operation parameters, e.g., a data rate and/orprotocol according to which data will be transferred over theconnection. Generally the negotiation procedure includes a plurality ofstages, such as one or more DP, EC and/or DC stages. Generally, the DPnegotiation stages include four negotiation stages, referred to also asphases 1-4, which include a protocol selection stage (e.g., according tothe V.8 protocol), and negotiation stages for training the DP, selectionof symbol and/or bit rates and determination of a round trip delay. TheEC and DC negotiation stages include, for example, an EC protocolnegotiation (V.42 or MNP5) stage and an ECDC parameter negotiation stage(e.g., selection of a compression format).

The negotiation stages are performed in accordance with protocols whichstate which signals are to be transmitted at what times. Some of thesignals must be transmitted within a short interval from the receptionof a control signal from the other party to the negotiation. Therefore,negotiating modems are generally connected over channels which have around trip delay beneath a required threshold.

After the negotiation stages, a data transfer stage is performed atwhich the modems modulate and demodulate the data packets they areprovided and pass the modulated signals over the connection. During boththe negotiation stage and the data transfer stage, signals aretransmitted on the connection in both directions at the same time, in anoperation mode referred to as full duplex. Generally, the pair of modemsincludes a call modem which initiates the formation of the connectionand an answer modem which responds to the initiative of the call modem.

During the data transfer stage, the modems employ provisions to cancelfar-echo effects. In addition, the EC layer in each of the modemsverifies, as described above, that all the data transmitted was properlyreceived and if necessary requires re-transmissions. For these tasks,the modems generally measure the round trip delay (RTD) of signalstransmitted between them during the negotiation stage of VBMconnections, for example during the second phase of the negotiationstage of the V.34 protocol. Similar methods to those described in theV.34 for determining the RTD are described in other protocols, such asthe V.90.

According to the V.34 protocol, at a specific time, the answer modeminitiates a phase reversal of a signal A it transmits. The call modemresponds with a phase reversal in a B signal it transmits, 40 msec afterdetecting the phase reversal in the A signal. Thereafter, the answermodem responds with a second phase reversal, 40 msec after detection ofthe phase reversal in the B signal. Accordingly, the call and answermodems independently calculate the RTD of the connection.

The telephone network is also used for fax connections. In faxconnections, image data is modulated onto voice signals, which aretransmitted over switched networks together with control information.Before transmission of signals, fax connections include a test stage inwhich the cap abilities of the connection are determined. The signals onthe fax connection, both during the test stage and during the datatransmission, are transmitted in only one direction in an operation modereferred to as half duplex. That is, at any time only one end unit faxmachine transmits signals on the connection.

Existing PSTN hardware cannot support the increasing demand for alltypes of communication services, and therefore additional hardware isadded to the PSTN instead of, or in addition to, the current hardware ofthe PSTN. In many cases, packet based networks are cheaper to installand maintain than switched networks. Therefore, telephony providers areadding many packet based lines and/or networks to their infrastructure,especially to their long distance infrastructure.

An exemplary hybrid telephone connection includes two switched segmentswhich connect end units, e.g., telephone sets, to respective gateways.The gateways, on the other hand, are connected through a packet basednetwork. The gateways receive streams of signals from the respective endunits, pack the streams, for example in a pulse code modulation (PCM)format into packets and pass the packets over the packet based networkto the other gateway. The other gateway unpacks the packets into astream of signals which is forwarded to the other end unit.

The travel time of packets through the packet based network may vary fordifferent packets of a single connection. Therefore, the gatewaysmaintain jitter buffers which delay the packet they receive over thepacket based network for a short period allowing the gateway to organizethe packets in their original order. When packets are not receivedwithin the short delay, the gateways generate filler signals to replacethe data in the delayed packet. If only a small percentage of packetsare delayed beyond the allowed period (or are otherwise lost), telephoneconversations are passed with sufficient quality such that the loss ofpackets is substantially unnoticed.

In some cases, fax signals are handled by gateways in the same way voicesignals are handled. However, the loss of a relatively small percent ofthe modulated signals is sufficient to prevent demodulation of thesignals. Therefore, in some gateways, when the gateway receives faxsignals, the gateway demodulates the signals and passes them to theother gateway in a predetermined packet format, for example as describedin the T.38 ITU-T recommendation, “Procedures for real-time Group 3facsimile communication over IP networks”, the disclosure of which isincorporated herein by reference. Gateways generally identify the faxsignals using methods such as described, for example, in U.S. Pat. No.RE35,740, the disclosure of which is incorporated herein by reference.The other gateway extracts the Fax data from the packets andre-modulates the Fax data for transmission to its respective end-unit.

It is noted that most VBM connections are local connections to Internetservice providers (ISP), which provide gateway services to packet-basednetworks. Nonetheless, there are cases when it is desired to create longdistance modem connections, for example, for remote access (RAS)applications.

SUMMARY OF THE INVENTION

An aspect of some embodiments of the present invention relates toforming a connection between two end modems over a hybrid link path,which includes at least one non-VBM segment. Such connection between twoend modems is referred to herein as a MoIP (modem over IP) connection.Gateways at opposite ends of the non-VBM segment demodulate signalsreceived from VBM segments and modulate signals transmitted on to theVBM segments.

In some embodiments of the invention, the MoIP connection includes asingle packet based segment and a pair of switched link paths whichconnect the modems to the packet based segment. In some embodiments ofthe invention, gateways on the edges of the packet based segmentsinclude modems which conduct separate VBM connections with the endmodems establishing the MoIP connection.

In some embodiments of the invention, the gateway modems perform fulltermination of the signals transmitted on their respective VBMconnections. The full termination includes data pump (DP) modulation anddemodulation, error correction, flow control, data compression and, whennecessary, requesting retransmission of data not properly received. Inthese embodiments, the VBM connections may operate independent of eachother, allowing the parameters (e.g., data rate, modem standard) of theVBM connections to be different for the different VBM connections.Between the gateways, on the packet based networks, the gatewaysoptionally perform flow control. Alternatively or additionally, thegateways use an acknowledgment scheme, redundancy transmissions and/or aforward correction scheme in order to minimize transmission errors.Further alternatively, higher protocol levels are trusted to ensureproper reception of the transmitted data.

In other embodiments of the invention, the gateways perform partialtermination, i.e., they perform data pump termination and partial orcomplete error correction (EC) termination but do not perform datacompression termination, on their respective VBM connections. Also inthese embodiments, the VBM connections may operate at different ratesand/or in accordance with different protocols. In addition, there maynot be any need to mirror retrain or other events occurring on one ofthe connections to the other connection. In some of these embodiments,however, at least some of the parameters of the connections arecorrelated, so as to minimize the time difference between thetransmission of the same data segment on the different VBM connections.Optionally, the entrance to the data phase of the VBM connections issynchronized between the connections, for example by at least partiallycorrelating the data pump training signals on the VBM connections.Alternatively or additionally, compression parameters exchanged at thebeginning of the data phase are passed between the gateways, such thatboth the VBM connections agree on the same compression parameters.Transmitting the signals on the packet based network in their compressedform reduces the bandwidth utilization of the packet based network. Inaddition, not performing DC termination substantially reduces powerconsumption and the memory consumption of the gateways.

In still other embodiments of the invention, the gateways perform onlyDP termination and do not perform error correction and data compression(ECDC) termination on their respective VBM connections. The bitsreceived by the gateways are transferred intact to the other gateway anderror correction and data compression are optionally managed by the endmodems of the MoIP connection. Not performing error detection and datacompression by the gateways substantially reduces the delay of thesignals on the MoIP connection, without affecting the transmissionspeed.

In some embodiments of the invention, the VBM connections between thegateways and their respective end units are correlated such that theyoperate in accordance with the same modem protocol and at the same datarate. Optionally, the gateways transmit to each other control packets,which include information they use in determining the modem protocoland/or data rates they plan to use on their VBM connection. In someembodiments of the invention, during negotiation stages of the MoIPconnection, the gateways send stalling signals, referred to as spoofingsignals, to their respective end modems until they receive input fromthe other gateway on the modem and link capabilities of the VBMconnection established by the other gateway. The stalling signals delaythe progression of the negotiation procedure without causing thetermination of the connection.

In an embodiment of the invention, during a V.8 connection whichrequires reception of two consecutive identical packets in order toproceed, the specific series of packets used to stall the connectionincludes a series of valid packets, which should be currentlytransmitted according to the standard, in which no two consecutivepackets have identical values.

Alternatively or additionally, the gateways lengthen the transmissiontime of one or more of the signals they transmit according to thestandard they are using. For example, in the V.8 standard, instead oftransmitting the JM signal immediately upon receiving a correct CMsignal, the gateway continues to transmit the ANSam signal until itreceives from the other gateway the information it needs in order totransmit the JM signal.

In some embodiments of the invention, rather than transmitting a seriesof packets which stalls the connection, a packet with probable values istransmitted, continuing the negotiation procedure. If, upon receivinginformation from the other connection, the values of the transmittedpacket are found not to conform to the other modem connection, a retrainis initiated and the negotiation process is re-started using thereceived information from the other modem connection.

In some embodiments of the invention, when a MoIP connection carriesfiller bits which do not represent information, the filler bits are notpassed on the packet based segment. Optionally, the gateways fill in themissing, filler bits based on control signals they receive from theother gateway and/or responsive to not receiving bits at the data rateof the connection.

An aspect of some embodiments of the present invention relates to atime-deception modem which causes a peer modem, with which it forms aVBM connection, to calculate a round trip delay (RTD) value differentfrom the delay between the two modems, in order to improve the qualityof the performance of the connection. Optionally, the peer modem is notaware of the deceptive actions of the time-deception modem.

In some embodiments of the invention, a VBM connection is a portion of amodem over IP (MoIP) connection. A typical MoIP connection is formed oftwo VBM connections which connect a call and an answer modem to twogateways which, in turn, are connected over an IP network. In someembodiments of the invention, one or both the gateways includetime-deception modems which cause the call and/or answer modems tocalculate an RTD value which estimates the round trip time over theentire MoIP connection rather than over the VBM connection to which thetime-deception modem is directly connected.

In some embodiments of the invention, the time-deception modem delaysthe transmission of a phase reversed signal for a correction period, inaddition to the 40 msec from receiving the phase reversal from the peermodem, prescribed in the V.34 protocol. In some embodiments of theinvention, the correction period comprises an earlier measured roundtrip delay period of the IP network connecting the two gateways andoptionally a predetermined RTD for VBM connections, which represents theRTD of the remote VBM connection of the MoIP connection. Alternatively,the time-deception modem mirrors the phase reversal by transmitting anappropriate message to the other gateway, and delays the transmission ofits response, phase reversed, signal until a response to the mirroredphase reversal is received.

An aspect of some embodiments of the present invention relates todistributing the tasks of a remote access server for VBM connectionsbetween two or more units which are located in different geographicallocations. Optionally, the two or more units are located in geographicallocations which are separated by hundreds or thousands of meters or evenhundreds or thousands of kilometers. In some embodiments of theinvention, the two or more units include a front end unit which performsthe data pump (DP) tasks and optionally one or more other tasks, e.g.,error correction (EC) tasks, and an upper layer unit which performs datacompression (DC) tasks and optionally one or more other tasks, e.g.,tasks not performed by the front end unit. Using this task distribution,the signals transmitted between the front end unit and the upper layerunit are already compressed, such that additional compression anddecompression tasks, which are generally computationally intensive, arenot required in the front end unit. The fact that the signalstransmitted between the front end unit and the upper layer unit arecompressed, is true even if one of the compressions of the DC modemlayer and the PPP protocol are not used, as may be standardized in thefuture.

Performing the tasks of the remote access server (RAS) in a plurality oflocations allows greater freedom in laying out apparatus of the RAS. Forexample, in some cases it is desired that modem connections beterminated as close as possible to the respective client modems, inorder to conserve expensive switched telephone lines. In such cases, inaccordance with embodiments of the invention, front end units whichperform only some of the tasks of a modem RAS are positioned at aplurality of locations close to the client modems while the remainingtasks are performed by an upper layer unit at a central location. Thus,the volume and maintenance costs of the apparatus at the plurality offront end locations is reduced as they perform only some of the tasks.In addition, centralizing the handling of some of the tasks reduces thecost of the apparatus performing these tasks, as the utilization rate ofapparatus at a central location is generally higher.

In some embodiments of the invention, distributing the tasks of a RASmay be used for Internet data off loading (IDOL). The off-loading unitsinclude only front end units (as described above) of a distributed RAS.The remaining tasks are performed by an upper layer unit (as describedabove) employed in an interface box of an Internet service provider(ISP).

In some embodiments of the invention, distributing the tasks of a RAS isperformed by an Internet service provider, in order to provide signaltermination close to the client modems on the one hand and concentrationof the upper layer tasks on the other hand.

In some embodiments of the invention, the distribution of the tasksbetween the two or more units is adjusted dynamically. Optionally, at aspecific time, the task distribution between the units for substantiallyall the handled connections, or for all the newly accepted connections,is the same. Alternatively, the task distribution for differentconnections may be different for different tasks.

Optionally, the task distribution is adjusted dynamically responsive tothe load on the two or more units. For example, when a front end unit isclose to its maximal capacity, the distribution is such as to requireminimal computation power from the front end unit. When on the otherhand, the load on the upper layer unit is high, the front end optionallytakes upon itself a larger portion of the tasks.

An aspect of some embodiments of the present invention relates todistributing the tasks of a modem between two or more units whichcommunicate through a packet based network, e.g., a wide area network(WAN), a metropolitan area network (MAN) and/or a local area network(LAN). Optionally, the packet based network comprises an IP network, aframe relay network and/or an ATM network.

An aspect of some embodiments of the present invention relates to afront end unit of a distributed modem that may operate with a pluralityof different upper layer units. In some embodiments of the invention, informing a connection, the front end unit is coupled with one of aplurality of upper layer units, for example, according to the telephonenumber dialed. Optionally, a single front end unit handles a pluralityof VBM connections concurrently, which connections pass throughdifferent upper layer units.

An aspect of some embodiments of the present invention relates tomanaging a VBM connection with uneven layers of handling on the oppositesides of the connection. On a first end of the connection, the data pumptasks are performed with a set of one or more additional modem taskswhile on a second end a different set including fewer modem tasks(optionally no tasks beyond the data pump tasks), is performed. Thesecond end of the connection optionally comprises a gateway whichforwards signals from the VBM connection over a non-VBM connection(e.g., a packet based connection) to an additional unit which is capableof handling partially terminated VBM signals. The additional unit maycomplete the termination of the partially terminated signals (i.e.,perform the layer tasks performed by the first end but not by the secondend) or may perform the same tasks as performed by the second end, inreverse, in order to transmit the signals over another VBM connection.In some embodiments of the invention, the second end of the VBMconnection handles both connections for which the termination iscompleted by the additional unit and connections for which theadditional unit reverses the tasks performed by the second end of theVBM connection. Optionally, the second end performs substantially thesame tasks regardless of the tasks performed by the additionalapparatus.

There is therefore provided in accordance with an embodiment of theinvention, a method of performing a negotiation session on a modemconnection, comprising receiving a plurality of negotiation signals fromthe source modem, by a first gateway, forwarding at least some of thereceived negotiation signals from the first gateway to a second gateway,over a packet based network, receiving, by the first gateway, responsesto the forwarded negotiation signals from the second gateway, forwardingthe responses from the second gateway to the source modem, by the firstgateway, and transmitting from the first gateway to the source modem,response signals to at least some of the received negotiation signals,without receiving a response to the at least some of the signals fromthe second gateway.

Optionally, forwarding the responses from the second gateway to thefirst modem comprises forwarding at least some of the responses withoutaltering their information content.

Optionally, forwarding the responses from the second gateway to thefirst modem comprises forwarding at least some of the responses with analtered information content.

Optionally, transmitting response signals from the first gateway to thesource modem comprises transmitting at least some of the responsesignals without forwarding the signals to which the response signalsrespond to the second gateway. Optionally, in response to at least someof the negotiation signals from the source modem, the first gateway bothtransmits response signals to the source modem and forwards thenegotiation signals to the second gateway. Optionally, transmittingresponse signals from the first gateway to the source modem comprisestransmitting at least some of the response signals after forwarding thesignals to which the response signals respond to the second gateway butbefore receiving a response thereto. Optionally, in response to at leastsome of the negotiation signals from the source modem, the first gatewayboth transmits response signals to the source modem, which include guessvalues of one or more parameters and forwards response signals from thesecond gateway which include final values of the one or more parameters.

Optionally, the method includes initiating a retrain by the firstgateway between transmitting the response signals to the first modem andforwarding the response signals from the second gateway. Optionally, thefirst gateway both transmits response signals to the source modem andforwards the negotiation signals to the second gateway substantiallyconcurrently.

Optionally, the signals to which the first gateway responds to thesource modem comprise DP negotiation signals. Optionally, the signalswhich the first gateway forwards to the second gateway comprise ECnegotiation signals. Optionally, the signals which the first gatewayforwards to the second gateway comprise signals for calculation of theround trip delay of the modem connection. Optionally, forwarding thenegotiation signals to the second gateway comprises forwardingsubstantially the same bit content. Alternatively, forwarding thenegotiation signals to the second gateway comprises forwarding only apartial portion of at least one of the received signals.

Optionally, forwarding the negotiation signals to the second gatewaycomprises forwarding over a network path which has a round trip delaygreater than the maximal time defined for responding to at least one ofthe negotiation signals from the source modem.

There is further provided in accordance with an embodiment of theinvention, a communication gateway, comprising a switched networkinterface adapted to receive a plurality of negotiation signals from asource modem, an addressable network interface adapted to forwardnegotiation signals to a remote gateway; and a controller adapted toforward through the addressable network interface substantially theentire bit content of at least some of, but not all, the negotiationsignals received through the switched network interface, during aspecific connection.

Optionally, the addressable network interface comprises a packet basednetwork interface.

There is further provided in accordance with an embodiment of theinvention, a communication gateway, comprising a switched networkinterface adapted to receive a plurality of negotiation signals from asource modem, an addressable network interface adapted to forwardnegotiation signals to a remote gateway; and a controller adapted toforward through the addressable network interface at least some of, butnot all, the negotiation signals received through the switched networkinterface during a specific connection and which is adapted to respondthrough the switched network interface to at least some of, but not all,the negotiation signals received through the switched network interfaceduring the specific connection.

Optionally, the controller is adapted to forward through the addressablenetwork interface substantially the entire bit content of at least someof the negotiation signals received through the switched networkinterface.

Optionally, the controller is adapted to forward through the addressablenetwork interface a portion including less than the entire bit contentof at least some of the negotiation signals received through theswitched network interface.

There is further provided in accordance with an embodiment of theinvention, a method of performing a non-facsimile modem negotiationsession on a modem connection by a gateway, comprising:

receiving negotiation signals of a plurality of stages from a sourcemodem, by the gateway; and

transmitting response signals, by the gateway, responsive to thereceived negotiation signals, when so required by the protocolsgoverning the stages, to the source modem,

wherein at least some of the response signals of a first group of atleast one of the stages are generated by the gateway, and wherein allthe response signals of a second group of at least one of the stages arereceived by the gateway from a separate unit.

Optionally, substantially all the response signals of at least one ofthe stages are generated by the gateway. Optionally, substantially allthe response signals of at least one of the stages are generated by thegateway without relation to information received from units other thanthe source modem. Optionally, transmitting response signals of thesecond group comprises transmitting the negotiation signals as if theyare data signals.

Optionally, the second group of stages comprises at least one ECDCnegotiation stage.

Optionally, the first group of stages comprises at least one DPnegotiation stage.

Optionally, the separate unit comprises a remote unit.

There is further provided in accordance with an embodiment of theinvention, a method of handling signals passing on a modem connection,by a gateway which connects a packet based segment and a switchedsegment of the connection, comprising listening to signals passing onthe connection, identifying on the connection a modem identificationsignal which notifies that the connection is going to carry modemsignals, operating in a first state, in which signals are transferredfrom the switched segment to the packet based segment without performingdemodulation, after the identifying of the modem identification signal;and operating in a second state, in which signals transferred from theswitched segment to the packet based segment are demodulated, afteroperating in the first state.

Optionally, the method includes deciphering the contents of at least oneof the signals passing on the connection, while the gateway operates inthe first state. Optionally, the method includes moving from the firststate to the second state responsive to the contents of at least one ofthe deciphered signals. Optionally, moving from the first state to thesecond state comprises moving at a point determined responsive to theidentified signals.

Optionally, moving from the first state to the second state comprisesmoving after completion of a V.8 negotiation phase.

Optionally, the method includes moving from the first state to thesecond state a predetermined time from the beginning of the connection.

Optionally, the deciphered signals comprise signals in accordance withthe V.8 protocol.

There is further provided in accordance with an embodiment of theinvention, a method of handling signals passing on a modem connection,by a gateway which connects a packet based segment and a switchedsegment of the connection, comprising:

operating in a first state, in which signals are transferred from theswitched segment to the packet based segment without performingdemodulation, after the identifying of the modem identification signal;and deciphering the contents of at least one of the signals passing onthe connection, while the gateway operates in the first state.

Optionally, deciphering the contents of at least one of the signalscomprises deciphering the contents of a signal in accordance with theV.8 protocol.

Optionally, the method includes determining whether to operate in asecond state, in which signals transferred from the switched segment tothe packet based segment are demodulated, responsive to the decipheredsignals.

Optionally, the method includes moving to the second state if thedeciphered signals indicate the use of a protocol supported by thegateway for transfer of data on the connection.

There is further provided in accordance with an embodiment of theinvention, a gateway, comprising:

a switched network interface adapted to receive modem signals;

an addressable network interface adapted to forward signals to a remotegateway;

an encapsulation unit adapted to forward through the addressable networkinterface, without demodulation, at least some of the modem signalsreceived by the switched network interface; and a demodulation unitadapted to demodulate and forward through the addressable networkinterface, at least some of the modem signals received by the switchednetwork interface. Optionally, the encapsulation unit is adapted toforward modem signals received during a protocol selection negotiationstage. Optionally, the encapsulation unit is adapted to forward modemsignals as PCM samples.

Optionally, the demodulation unit is adapted to forward modem signalsreceived after the completion of a protocol selection negotiation stage.

There is further provided in accordance with an embodiment of theinvention, a method of establishing a modem connection over a hybridnetwork path, comprising:

selecting at least two gateways to perform format conversion of signalstransmitted between segments of the modem connection over the hybridnetwork path; and

performing a negotiation session between the selected at least twogateways, so as to select a format of signals transmitted between theselected gateways.

Optionally, performing the negotiation session comprises determiningwhether the signals transmitted between the gateways are compressed inaccordance with a modem-compression protocol.

There is further provided in accordance with an embodiment of theinvention, a method of transmitting non-facsimile data signals between asource modem and a destination modem, comprising transmitting the datasignals from the source modem, over a first switched network path, to afirst gateway, demodulating the data signals at the first gateway,transmitting at least some of the demodulated data signals from thefirst gateway to a second gateway, over a packet based network,modulating the data signals at the second gateway, and transmitting themodulated data signals from the second gateway over a second switchednetwork path to the destination modem.

Optionally, transmitting the data signals from the first gateway to thesecond gateway comprises transmitting compressed data signals, which arecompressed according to a modem compression format. Optionally, thesource modem compresses the signals and the first gateway transfers thesignals without decompression.

Optionally, transmitting the data signals comprises transmitting signalscompressed according to the V.44 protocol.

Optionally, transmitting the data signals from the first gateway to thesecond gateway comprises transmitting the data signals along with anymodem error correction fields received from the source modem.

Optionally, transmitting the data signals from the first gateway to thesecond gateway comprises transmitting the data signals along with anymodem filler bits received from the source modem.

Optionally, transmitting the data signals from the first gateway to thesecond gateway comprises transmitting the data signals along with anyLAPM acknowledgment fields received from the source modem.

Optionally, the method includes performing one or more LAPM tasks on thedemodulated signals, by the first gateway, before transmitting thesignals to the second gateway. Optionally, the method includesperforming one or more HDLC tasks on the demodulated signals, by thefirst gateway, before transmitting the signals to the second gateway.Optionally, the signals are transmitted on the first switched networkpath to the first gateway at the same rate as the signals aretransmitted from the second gateway on the second switched network path.

Optionally, the signals are transmitted on the first switched networkpath to the first gateway at a different rate than the signals aretransmitted from the second gateway on the second switched network path.

Optionally, transmitting at least some of the data signals over a packetbased network comprises transmitting over an IP network. Optionally,transmitting at least some of the data signals over a packet basednetwork comprises transmitting over a connection which does not providedelivery confirmation. Optionally, transmitting at least some of thedata signals over a packet based network comprises transmitting over aconnection which provides delivery confirmation. Optionally,transmitting at least some of the data signals over a packet basednetwork comprises transmitting over an ATM network. Optionally,transmitting at least some of the data signals over a packet basednetwork comprises transmitting over an addressable network. Optionally,transmitting at least some of the demodulated data signals comprisesdetermining, by the first gateway, whether the data signals receivedfrom the first modem have an information content and not transmitting atleast some of the signals determined not to have an information content.

Optionally, the method includes transmitting data signals from thedestination modem, over the second switched network path, to the secondgateway, demodulating the data signals at the second gateway,transmitting at least some of the demodulated data signals from thesecond gateway to the first gateway, over the packet based network,modulating the data signals at the first gateway, and transmitting themodulated data signals from the first gateway to the source modem.

Optionally, the signals transmitted on the second switched network pathto the second gateway are transmitted at the same rate as the signalsare transmitted from the first gateway on the first switched networkpath to the source modem.

Optionally, the signals are transmitted on the second switched networkfrom and to the destination modem, concurrently. Optionally, the firstand second switched network paths carry the same bit content of signals.Optionally, the signals transmitted on the first and second switchedpaths carry the same information. Optionally, the transmitted signalscomprise IP packets and wherein the IP packets transmitted on the firstand second switched paths carry identical IP headers. Optionally, thesource and destination modems comprise server modems.

Optionally, the source and destination modems comprise client modems.

Optionally, one of the source and destination modems comprises a clientmodem and the other of the source and destination modems comprises aserver modem.

Optionally, the data signals are received by the destination modem in amaimer which does not allow determination of whether the signals werepassed on the packet based network path or were passed on a singleswitched path.

Optionally, transmitting the packets over the packet based network tothe second gateway comprises regulating the delay of the packetsprovided to the second gateway.

There is further provided in accordance with an embodiment of theinvention, a method of transmitting data signals between a source modemand a destination modem, comprising transmitting the data signals fromthe source modem, over a first switched network path, to a firstgateway, demodulating the data signals at the first gateway,transmitting at least some of the demodulated data signals from thefirst gateway to a second gateway, remote from the first gateway, overan intermediate path, modulating the data signals at the second gateway;and transmitting the modulated data signals from the second gateway overa second switched network path to the destination modem.

Optionally, the first and second gateways are not in the same room.Optionally, the first and second gateways are distanced from each otherby at least 100 meters. Optionally, the first and second gateways aredistanced from each other by at least 10 kilometers. Optionally, theintermediate path comprises a path on an addressable network, a packetbased network and/or a DCME network. Optionally, transmitting at leastsome of the demodulated data signals from the first gateway to thesecond gateway comprises transmitting encrypted signals.

There is further provided in accordance with an embodiment of theinvention, a gateway for transferring voice band modem, non-facsimile,signals between a switched network and a packet based network,comprising a switched network interface adapted to transmit and receivemodulated modem signals on a switched network path, a data pump adaptedto modulate signals transmitted by the switched network interface anddemodulate signals received by the switched network interface, a packetinterface adapted to transmit and receive signals on a packet basednetwork connection; and a controller adapted to establish a connectionbetween a switched network path and a packet based network connection,before data signals are transmitted on the switched network path, and toforward at least some of the data signals passing on the logicalconnection between the packet interface and the data pump.

Optionally, the gateway does not perform modem compression ordecompression on the data signals passing on the logical connection.Optionally, the packet interface is adapted to encapsulate data signalsit transmits in packets having IP headers which are not related topossible IP headers included in the demodulated signals. Optionally, thecontroller forwards substantially all the data signals passing on thelogical connection, between the packet interface and the switchednetwork interface.

Optionally, the controller does not forward data signals which do notcarry information.

Optionally, the gateway does not perform modem flow control tasks on thedata signals passing on the logical connection. Optionally, the gatewaydoes not perform modem error correction tasks on the data signalspassing on the logical connection. Optionally, the gateway does notremove filler bits from the data signals passing on the logicalconnection. Optionally, the modem is adapted to apply error correctiontasks to data signals passing on the logical connection. Optionally, thedata pump modulates and demodulates data signals substantiallyconcurrently.

There is further provided in accordance with an embodiment of theinvention, a system for transmission of modem, non-facsimile, signalsover a packet based network, comprising a first gateway adapted toreceive data signals from a first modem, to demodulate the received datasignals and to transmit the demodulated data signals over a packet basednetwork and a second gateway adapted to receive the data signalstransmitted from the first gateway over the packet based network, tomodulate the signals and to transmit the data signals to a second modem.Optionally, the first gateway is adapted to receive data signals fromthe second gateway, concurrently with the transmission of data signalsto the second gateway.

Optionally, the first gateway is adapted to transmit the demodulatedsignals to the second gateway without decompressing the signals.Optionally, the first gateway is adapted to transmit the demodulatedsignals along with one or more fields of an EC modem layer with whichthe signals were received from the first modem.

There is further provided in accordance with an embodiment of theinvention, a method of correlating parameters of a plurality of voiceband modem (VBM) connections, comprising beginning a negotiation stageof a first VBM connection, beginning a negotiation stage of a second VBMconnection, receiving values of one or more parameters of the secondconnection by an end unit of the first connection, and completing thenegotiation stage of the first connection based on the one or moreparameters of the second connection. Optionally, the method includestransmitting stalling signals on the first connection by the end unit ofthe first connection until the values of the one or more parameters ofthe second connection are received by the end unit.

Optionally, transmitting stalling signals comprises lengthening thetransmission of a control signal beyond a necessary transmission time ofthe control signal. Optionally, lengthening the transmission of thecontrol signal beyond its normal transmission time comprisestransmitting the control signal after the reception of a signal whichnormally causes the termination of the transmission of the controlsignal. Optionally, the negotiation stage comprises a data pumpnegotiation stage and/or an error correction negotiation stage.

Optionally, the method includes transmitting one or more control signalswith guess values during the negotiation stage and wherein completingthe negotiation stage comprises retransmitting the one or more controlsignals with values based on the one or more parameters of the secondconnection. Optionally, the method includes retraining the firstconnection before completing the negotiation stage.

There is further provided in accordance with an embodiment of theinvention, a method of calculating a round trip delay of signals on amodem connection, comprising transmitting a first time measurementsignal from a first modem to a second modem, transmitting a second timemeasurement signal from the second modem to the first modem, at aninterval after the reception of the first time measurement signal by thesecond modem, and calculating, by the first modem, a round trip delayvalue as the period between transmitting the first time measurementsignal and receiving the second time measurement signal, minus a delayperiod which is substantially different from the interval.

Optionally, the first and second modems are connected through a networksegment which segment is a portion of a composite connection includingat least one additional network segment and wherein calculating theround trip delay comprises calculating the round trip delay of thecomposite connection. Optionally, the at least one additional networksegment comprises a switched network segment and a packet based networksegment and wherein transmitting the second time measurement signalcomprises transmitting the second signal after an interval which is asum of the delay period, a round trip delay value of the switchednetwork segment and a round trip delay value of the packet based networksegment.

Optionally, the round trip delay value of the packet based networksegment comprises a value measured during the modem connection beforereceiving the first time measurement signal by the second modem.Optionally, the round trip delay value of the switched network segmentcomprises a predetermined estimate value. Optionally, the predeterminedestimate value comprises a maximal round trip delay value ofsubstantially all switched network segments which may appear in a pathbetween the first and second modems. Optionally, transmitting a secondtime measurement signal comprises transmitting a third time measurementsignal on the at least one additional network segment, receiving aresponse thereto and transmitting the second time measurement signalafter receiving the response.

BRIEF DESCRIPTION OF FIGURES

Particular non-limiting embodiments of the invention will be describedwith reference to the following description of embodiments inconjunction with the figures. Identical structures, elements or partswhich appear in more than one figure are preferably labeled with a sameor similar number in all the figures in which they appear, in which:

FIG. 1 is a schematic illustration of a hybrid modem connection usefulin illustrating an embodiment of the present invention;

FIG. 2 is a schematic block diagram of gateways in a composite modemconnection, in accordance with an embodiment of the present invention;

FIG. 3 is a schematic block diagram of gateways in a composite modemconnection, in accordance with another embodiment of the presentinvention;

FIG. 4 is a schematic time chart of the operations performed in thefirst phase of establishing a composite modem connection, in accordancewith an embodiment of the present invention;

FIG. 5A is a time chart of the operations performed following the firstphase of a composite modem connection, in accordance with an embodimentof the present invention;

FIG. 5B is a time chart of the operations performed during are-negotiation event, in accordance with an embodiment of the presentinvention;

FIGS. 6A and 6B are a time chart of the operations performed during asecond phase of a V.34 negotiation connection, in accordance with anembodiment of the present invention;

FIG. 7 is a schematic block diagram of gateways on a compositeconnection, in accordance with another embodiment of the presentinvention;

FIG. 8 is a time chart of signals transmitted on a MoIP connectionduring a compression negotiation stage, in accordance with someembodiments of the present invention;

FIGS. 9A, 9B and 9C describe three exemplary scenarios of ECDC parameternegotiation, in accordance with some embodiments of the presentinvention;

FIG. 10 is a flowchart of the acts performed by a gateway uponestablishing a connection, in accordance with an embodiment of thepresent invention;

FIG. 11 is a block diagram of a pair-gain system, in accordance with anembodiment of the present invention;

FIG. 12 is a block diagram of the pair-gain system of FIG. 11 includingdetails of a repeater thereof, in accordance with an embodiment of thepresent invention;

FIGS. 13A-13C are a flowchart of the acts performed by a repeater in apair-gain system, in accordance with an embodiment of the presentinvention;

FIG. 14 is a schematic illustration of a distributed remote accessserver (RAS) system, in accordance with an embodiment of the presentinvention;

FIG. 15 is a schematic block diagram of a public switching telephonenetwork (PSTN) with off-loading capabilities, in accordance with anembodiment of the present invention; and

FIG. 16 is a flowchart of the acts performed by a central office (CO) inaccepting a connection, in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic illustration of a MoIP connection 30, inaccordance with an embodiment of the present invention. A call modem 32Aestablishes a connection with an answer modem 32B, which connection isformed of three segments in series. In some embodiments of theinvention, modems 32A and 32B are both server modems or both digitalmodems. Alternatively, one of modems 32A and 32B is a client modem andthe other modem is a server modem.

A first segment of the MoIP connection passes on a switched network 34Abetween call modem 32A and a call gateway 36A. A second segment connectscall gateway 36A and an answer gateway 36B through a packet basednetwork 38. A third segment connects answer gateway 36B and answer modem32B on a switched network 34B. In some embodiments of the invention, thefirst and third segments carry the same data signals, although they maycarry different control signals. That is, if the data signalstransmitted between modems 32A and 32B comprise, for example, IPpackets, the headers of the IP packets on the first and third segmentsare identical, e.g., the TTL field has the same value. Alternatively,the first and third segments carry the same bits which containinformation, although filler data signals which do not carry informationmay be sent differently on the different segments.

In some embodiments of the invention, packet based network 38 has atleast a predetermined quality of service (QoS) level, i.e., a relativelylow packet loss rate, delay and/or jitter, in order to provideacceptable communication levels of service. Alternatively oradditionally, one or more redundancy methods, such as duplicatetransmission of some or all of the packets and/or use of a forward errorcorrection code are used to enhance the reliability of network 38.

In some embodiments of the invention, packet based network 38 comprisesa multipoint network which connects three or more communicationnetworks. In some embodiments of the invention, gateways 36A and 36B arenot included in a single casing or in the same room. Furthermore,gateways 36A and 36B may be distanced by hundreds, thousands or tens ofthousands of meters or even tens of kilometers or even more, for examplewhen packet based network 38 passes through a satellite or other outerspace transmission unit. In some embodiments of the invention, the roundtrip transmission time of signals on packet based network 38 betweengateways 36A and 36B is greater than the shortest response time definedfor modem negotiation signals in a protocol used to transmit signalsbetween modems. It is noted that the distance between gateways 36A and36B may affect the specific embodiments (of those described below) used,due to the affect of the distance on the round trip delay of signalsbetween modems 32A and 32B.

Optionally, packet based network 38 comprises an IP network.Alternatively or additionally, packet based network 38 comprises a cellbase network, such as an asynchronous transfer mode (ATM) network,and/or a frame relay network.

In an embodiment of the present invention, connection 30 is establishedusing connection establishment procedures substantially as used forestablishing voice over IP (VoIP) connections, for example, theprocedures of the H.323 protocol and/or the session initiation protocol(SIP). In establishing the connection, one or more packet connections ofa packet transport protocol (e.g., transmission control protocol (TCP)or user datagram protocol (UDP)) are established on packet based network38. The connection is optionally established by modems 32A and 32B andgateways 36A and 36B at the initiative of the modems, although otherinitiators of the connection may also be considered.

Optionally, in forming the connection, call modem 32A transmits a modemidentification signal which notifies modem 32B that the connection is amodem connection. A network controller identifies the modemidentification signal and accordingly chooses gateways 36A and 36B tobelong to the path which handles the connection. Alternatively oradditionally, gateways 36A and/or 36B identify the modem identificationsignal and accordingly set their operation mode. For example, thenotification may be based on the telephone number dialed which isincluded in a list of modem numbers. Alternatively or additionally,gateways 36A and 36B recognize that the connection is a modem connectionbased on, for example, the 2100 Hz signal which is transmitted at thebeginning of the use of the connection.

In some embodiments of the invention, call modem 32A and/or answer modem32B are standard modems which are not altered in order to perform thepresent invention. Furthermore, in some embodiments, call modem 32A andanswer modem 32B do not know whether they are connected directly over aswitched line or through gateways 36A and 36B.

Call modem 32A and/or answer modem 32B may be connected to switchednetwork 34B through any switched lines, analog or digital.

FIG. 2 is a schematic block diagram of gateways 36A and 36B and theconnection between them, in accordance with an embodiment of the presentinvention. Gateways 36A and 36B include gateway modems 40A and 40B whichcommunicate with modems 32A and 32B over switched networks 34A and 34B,respectively. Gateway modems 40 include data pumps 42 which modulate anddemodulate the signals passed on switched networks 34A and 34B, errorcorrection (EC) layers 43 and data compression (DC) layers 44. Errorcorrection layers 43 add CRC fields to transmitted data, check that datais received correctly, request retransmission of bits which were notreceived correctly and manage flow control. Data compression layers 44perform compression and decompression of the signals transmitted onswitched networks 34. Each of gateways 36 also includes an IP interface48 (marked 48A, 48B) which communicates with the interface 48 in theother gateway through packet based network 38. As is known in the art,each packet transmitted over packet based network 38 comprises a headerwhich identifies the connection to which it belongs. Thus, IP interface48 may receive packets belonging to a plurality of different connections30 and sort them out according to their headers.

In some embodiments of the invention, IP interfaces 48A and 48Bcommunicate over a connection of a delivery confirming protocol, such asover a TCP connection 50 established within packet based network 38.Alternatively, a connection of a non-delivery confirming protocol, suchas UDP, is used, optionally with complimentary flow control, forwardcorrection codes and/or complete higher level delivery confirmation.Further alternatively, higher levels at the ends of modems 32A and 32Bare trusted to check that no data was lost on packet based network 38.

In some embodiments of the invention, data signals received by either ofunits DC layer 44 and IP interface 48 are passed directly to the otherunit (of DC layer 44 and IP interface 48) within the same gateway, forforwarding to their destination. Control packets or signals, on theother hand, are examined, for example, by a controller 46 whichdetermines which actions are to be performed responsive to the controlsignals and whether the control signals should be forwarded by the otherunit, as described in detail in the following description.

A negotiation stage begins with call modem 32A (FIG. 3) sending a callsetup signal (e.g., CI of the V.8) over connection 30 to answer modem32B. The call setup signal is received by modem 40A of call gateway 36Awhich responds on switched network 34A according to the predeterminedprocedures agreed between modems 32A, 32B and 40, e.g., according to oneor more of the ITU-T V-series recommendations (for example as describedin the V.8 recommendation). In addition, controller 46A sends, throughIP interface 48A of call gateway 36A, a control packet to IP interface48B of answer gateway 36B. Responsive to receiving the control packet,controller 46B of gateway 36B instructs its modem 40B to send a callsetup signal to answer modem 32B and continue the procedures ofnegotiation and training, as is known in the art.

In some embodiments of the invention, the training and negotiatingprocedures (e.g., the four DP negotiation stages (phases 1-4), ECDCprotocol negotiation, ECDC parameter negotiation) of modems 32A and 40Aand of modems 32B and 40B are performed independently of each other andthe data in control signals passed during the negotiation is not passedover TCP connection 50. Therefore, in these embodiments, the connectionsbetween modems 32A and 40A and modem 32B and 40B may be at differentrates and even according to different protocols. Optionally,renegotiation and retraining procedures performed on one modemconnection do not affect the other modem connection.

In some embodiments of the invention, DC layer 44 includes a bufferwhich stores the data received from IP interface 48, when it is receivedat a rate faster than can be sent on the modem connection. Alternativelyor additionally, IP interface 48 maintains a buffer for the signalsbeing passed to DC layer 44.

In some embodiments of the invention, only if the negotiating fails,e.g., between modems 32A and 40A, gateway 36A notifies gateway 36B sothat it will disconnect the connection between modems 32B and 40B.Likewise, when one of call and answer modems 32A and 32B terminate theirmodem connection, the respective gateway notifies the other gateway sothat it will also terminate the other modem connection. The notificationmay be performed, for example, by closing the TCP connection 50 betweenthe gateways. In an embodiment of the invention, when one of the modemconnections is terminated the other modem connection is immediatelyterminated. Alternatively, the other modem connection is maintained fora predetermined period in case the terminated connection is promptlyreestablished.

Alternatively to performing the training and negotiation proceduresseparately, one or more of the negotiation stages is correlated betweenthe connections of modems 32A and 40A and of modems 32B and 40B, forexample, as described hereinbelow with reference to FIGS. 4, 5A and 5B.

Alternatively, to using a single TCP connection 50 for communicationbetween IP interfaces 48, separate TCP connections are used for control(e.g., setup negotiation signals) and data messages.

In some embodiments of the invention, IP interfaces 48 compress the datasignals they transmit and decompress the data signals they receive, inaccordance with any compression method, such as methods used on VBMconnections. Thus, the bandwidth utilization on packet based network 38is reduced.

FIG. 3 is a schematic block diagram of gateways 36A and 36B and theconnections between them, in accordance with another embodiment of thepresent invention. In the embodiment of FIG. 3, gateways 36A and 36Binclude IP interfaces 48 and controllers 46 similar to that describedabove, but include modems 60 (marked 60A and 60B) which do not performerror correction and data compression (ECDC) termination. Instead, datasignals are passed through gateways 36A and 36B without delay and the ECand DC termination are performed between call and answer modems 32A and32B. In some embodiments of the invention, IP interfaces 48 exchangesignals using one or more connections of a protocol which does notprovide delivery confirmation, e.g., UDP. Alternatively or additionally,IP interfaces 48 use one or more methods to increase the reliability ofthe transmissions on network 38, such as repeated transmission,redundancy codes and/or partial and/or total reception confirmation. Thesignals passing between IP interfaces 48 may include CRC fields used byend modems 32A and 32B in EC termination and/or are compressed inaccordance to data compression methods. Optionally, parameternegotiation and/or protocol negotiation frames which are exchanged atthe beginning of the data phase of an MoIP connection are related to bygateways 36A and 36B as regular data signals.

Not performing ECDC by gateways 36, reduces the signal delay overconnection 30. In an exemplary embodiment, the transmission time fromcall modem 32 to answer modem 32B is about 100 msec when ECDC is notperformed by gateways 36A and 36B, while when ECDC is performed by thegateways and the TCP protocol is used for transmission between IPinterfaces 48, about an additional 250 msec are added to thetransmission time, under normal conditions.

Furthermore, not providing ECDC by modems 60 simplifies the modems andreduces their power consumption. It is noted that modem 60 may be partof a modem array. By not performing ECDC by modem 60, the number ofconnections handled by the modem array is substantially larger than ifECDC is performed.

In an embodiment of the invention, IP interfaces 48 exchange datasignals on a UDP connection 70 and control signals on a TCP connection72. Alternatively, the control signals are exchanged on a UDPconnection; either the same connection as used for the data or aseparate connection is used. Optionally, some or all of the controlmessages are transmitted a plurality of times, e.g., three to fivetimes, to ensure that the control messages are received. In someembodiments of the invention, the number of times the control messagesare transmitted depends on the importance of the messages.

Modems 60 generally include data pumps 42 which modulate and demodulatethe signals which pass through gateways 36A and 36B. In some embodimentsof the invention, modem 60 checks the contents of the demodulatedsignals and transfers data signals directly to IP interface 48 to besent to the peer gateway through packet based network 38. Demodulatedcontrol signals are transferred to controller 46 for handling as is nowdescribed.

In some embodiments of the invention, during the negotiation, gateways36A and 36B ensure that the connections on networks 34A and 34B followthe same protocols and operate at the same upstream rates and the samedownstream rates (the upstream and downstream rates are not necessarilythe same). Alternatively, gateways 36A and 36B ensure that in theupstream from call modem 32A to answer modem 32B the data rate of theconnection from gateway 36B to answer modem 32B is greater than the datarate of the connection from call modem 32A to gateway 36A. In thisalternative the downstream from answer modem 32B to call modem 32A, thedata rate of the connection from gateway 36A to call modem 32A isgreater than the data rate of the connection from answer modem 32B togateway 36B. This alternative is, however, wasteful in bandwidth and/orin processing resources and requires that modems 32A, 32B and 60 supportan asynchronous transmission mode.

In some embodiments of the invention, gateways 36A and 36B includeoptional jitter buffers 58 which delay the data packets transmitted onUDP connection 70 for a predetermined time in order that substantiallyall the data packets passed on the UDP connection undergo equal delay.In some embodiments of the invention, jitter buffers 58 are relativelylarge relative to jitter buffers used for VoIP, such that even if thereis a drift in one of the clocks of switched networks 34A or 34B thejitter buffers will not overflow or underflow frequently. Alternativelyor additionally, the sizes of jitter buffers 58 are determined based onthe current delay and/or loss rate of packet based network 38, usingmethods known in the art for VoIP.

FIG. 4 is a schematic time chart of the operations performed by call andanswer modems 32A and 32B and gateways 36A and 36B of FIG. 3, in thefirst phase of establishing a connection, in accordance with anembodiment of the present invention. As is known in the art, ininitiating a connection according to the V.8 standard, call modem 32Asends, after a second, CI signals 80 along switched network 34A. CIsignals are received by modem 60A (FIG. 3) of gateway 36A whichresponds, as required by the V.8 recommendation, with the ANSam signal82, as defined by the V.8 standard. Substantially in parallel, IPinterface 48A sends a CI-RECV packet 84 to IP interface 38B, over TCPconnection 72. CI-RECV packet 84 notifies IP interface 48B that CIsignals 80 were received. Upon receiving CI-RECV packet 84, IP interface48B notifies controller 46B which instructs modem 60B to start sendingCI signals 86 to answer modem 32B.

When answer modem 32B detects at least one CI signal 86, it respondswith an ANSam signal 88 as defined by the V.8 recommendation. In someembodiments of the invention, modem 60B does not respond to ANSam signal88 until gateway 36B receives from gateway 36A information on the VBMconnection between modem 60A and call modem 32A, as describedhereinbelow. Rather, modem 60B continues to transmit CI signal 86 evenafter ANSam signal 88 is received. According to the V.8 recommendation,modem 32B continues to transmit ANSam signal 88, for up to about 5seconds, until modem 60B responds to ANSam signal 88.

In some embodiments of the invention, when modem 60B receives ANSamsignal 88, an ANSam-RECV packet 102 is sent by IP interface 48B to IPinterface 48A.

After receiving ANSam signal 82 from modem 60A, call modem 32A transmitsCM signals 90 as defined by the V.8 standard In some embodiments of theinvention, modem 60A continues to transmit ANSam signal 82 even after itreceives CM signals 90, in order to stall the VBM connection on switchednetwork 34A until gateway 36A receives information on the VBM connectionon switched network 34B from gateway 36B as described hereinbelow.

Upon receiving CM signal 90, in some embodiments of the invention, IPinterface 48A sends to IP interface 48B a CM-RECV message (not shown)which indicates that a CM signal 90 from call modem 32A was received.Alternatively or additionally, CM signal 90 is passed to controller 46(FIG. 3) for decoding. When controller 46 finishes decoding the CMsignal, call IP interface 32 sends a CM-CONTENT message 98 carrying thecontents of the received CM signal 90, to IP interface 48B. In anembodiment of the invention, CM-CONTENT message 98 also includes thecapabilities of modem 60A. Alternatively or additionally, CM-CONTENTmessage 98 includes the standards and/or other capabilities supported byboth call modem 32A (as indicated in CM signal 90) and modem 60A

When CM-CONTENT message 98 is received by IP interface 48B, its contentsare passed to controller 46B which instructs modem 60B as to whichcontents it should include in the CM signal it transmits. Upon receivingthe instructions, modem 60B immediately, or after a predeterminedperiod, begins to transmit a series 104 of identical CM messagescontaining the contents instructed by controller 46B.

In some embodiments of the invention, the contents of the CM messages inseries 104 are based on the common capabilities of modems 60A, 60B, andcall modem 32A. Thus, it is assured that the connections on networks 34follow the same protocol.

When answer modem 32B receives two identical consecutive CM signals fromseries 104, it responds with JM signals 106 as required by the V.8recommendation. Responsive to JM signal 106, gateway 36B transmits theCJ signal 108 and the connection between modem 60B and answer modem 32Bmoves to the second phase of negotiation, as is known in the art.

Substantially in parallel to transmitting CJ signal 108, gateway 36Bsends a JM-CONTENT packet 110 which carries the capabilities of answermodem 32B and optionally of modem 60B. In some embodiments of theinvention, JM-CONTENT packet 110 has the same format as CM-CONTENTpacket 98. Upon receiving JM-CONTENT packet 110, gateway 36A sends aseries of identical JM signals 112, based on the information received inJM-CONTENT packet 110 and optionally the capabilities of modem 60A.Thereafter, call modem 32A responds with a CJ signal 114, as is known inthe art, and the connection on network 34A moves into the second phaseof negotiation as is known in the art.

Further alternatively or additionally, modem 60B does not transmit CIsignals 86 immediately upon receiving CI-RECV packet 84. Instead, modem60B transmits CI signals 86 only after CM-CONTENT packet 98.Alternatively or additionally, modem 60B transmits CI signals 86 after apredetermined delay such that CM-CONTENT packet 98 will be received atabout the time when CM signals 104 should be transmitted.

In some embodiments of the invention, CI-RECV packet 84, ANSam_RECV 102,CM_CONTENT 98, JM_CONTENT 110 and/or other packets transmitted overpacket based network 38, are substantially in accordance with thedefinitions of packets in the T.38 recommendation. Alternatively oradditionally, any other conventions agreed between gateways 36A and 36Band which are compatible with network 38 are used.

FIG. 5A is a time chart of the operations performed during the second tofourth phases of a negotiation connection in which the V.34 protocol waschosen in the first phase, in accordance with an embodiment of thepresent invention. In some embodiments of the invention, each pair ofmodems 32A and 60A and modems 32B and 60B independently performs phases2 and 3 of the standard negotiation procedures. Alternatively, gatewaymodems 60A and 60B perform phase 2 and/or phase 3 negotiations in amanner which differs from the standard. In some embodiments of theinvention, gateway modems 60A and 60B perform phase 2 as describedhereinbelow with reference to FIGS. 6A and 6B, so that the round tripdelay (RTD) calculated by modems 32A and/or 32B will reflect the delayof the entire path between modems 32A and 32B and not only the pathbetween modems 32A and 32B and the respective gateway modems 60A and 60Bto which they are directly connected.

In some embodiments of the invention, gateways 36A and/or 36B supportall the symbol rates of the V.34 protocol so as to allow maximal symbolrate leeway to end modems 32A and 32B. In some embodiments, the symbolrates used on networks 34A and 34B are determined independent of eachother during phase-2, such that the symbol rate used by the connectionon network 34A may be different than the connection on network 34B. Ifthe different symbol rates on networks 34A and 34B do not allow theconnections on networks 34A and 34B to use the same bit rate, theconnections are retrained (i.e., the connections are moved back to phase2), forcing the connections to agree on a single symbol rate, e.g., thelower of the previously agreed symbol rates on networks 34A and 34B. Thechances of the different symbol rates on networks 34A and 34B preventingthe connections on networks 34A and 34B from using the same bit rate arerelatively slight and therefore in these embodiments, the risk ofrequiring a retrain is taken in order to allow use of higher bit rates,i.e., above the bit rate of 21,800 which is the maximal bit rate allowedby the 2400 symbol rate in the V.34 protocol.

Alternatively or additionally, gateways 36A and/or 36B deliberately donot identify themselves as supporting symbol rates and/or other phase-2or phase-3 parameters which may not allow the connections on networks34A and 34B to reach the same transmission bit rate without-changing,their symbol rates. In an embodiment of the invention, gateways 36Aand/or 36B identify themselves as supporting only the lowest symbolrate, i.e., 2400 symbol/sec. Thus, in case one of networks 34 can onlysupport a bit rate of 2400 or 2600, the other network 34 will be able toestablish a connection at the same bit rate.

In some embodiments of the invention, gateways 36A and/or 36B do notgenerally limit the symbol rates of the connections on networks 34A and34B. However, if a retrain is required, gateways 36A and/or 36B note theidentity (e.g., telephone number) of the modem which requires low bitrates of only 2400 or 2600 and subsequent connections to this modem areperformed while forcing use of the 2400 symbol rate. Optionally, theforcing of the use of the 2400 symbol rate is performed only after apredetermined number of connections which required a retrain and/or thetime extent of the symbol rate forcing is limited in case the networkconnection to the modem is improved.

Alternatively, gateways 36A and 36B make sure that the connections onnetworks 34A and 34B operate with the same symbol rate, using any of themethods described hereinbelow for equalizing the bit rates of thenetworks.

In the fourth phase, as defined in the V.34 recommendation, modems 32A,32B, 60A and 60B transmit TRN signals 120 and 121. Thereafter, modems32A and 32B transmit MP signals 122 which identify the capabilities ofthe transmitting modems. In some embodiments of the invention, modems60A and 60B do not immediately transmit MP signals 130 but instead waituntil they determine the capabilities of the connection of the othergateway. In order not to leave the connections silent (which may causedisconnection), in some embodiments, modems 60A and 60B continue totransmit the TRN signals 120 until they receive the information requiredto generate the MP signals.

Upon receiving the MP signals 122 from modems 32A and 32B, respectively,gateways 36A and 36B transmit to each other, over packet based network38, modem training report (MTR) packets 126. MTR packets 126 identifythe capabilities of modems 32A and 32B, respectively, as identified inthe MP signals 122 they transmitted. In an embodiment of the invention,MTR packets 126 also identify the capabilities of the modem of thetransmitting gateway 36. Upon receiving an MTP packet 126 from the othergateway 36, the gateways (e.g., 36A) stop transmitting the TRN signals120 and generate and transmit MP signals 130 which identify the commoncapabilities of the modem 32 to which they are not connected (e.g., 32A)and the modems 60 of the gateways. Thereafter, the negotiationprocedures of the connections on networks 34A and 34B are completedindependently according to the V.34 recommendation.

The contents of MP signals 130 are chosen such that the operation rateschosen in accordance with the V.34 recommendation are supported by allthe modems. Thus, the rates of operation of the connections on networks34A and 34B are substantially identical. In an embodiment of theinvention, the contents of MP signals 130 are chosen as the commoncapabilities of the generating gateway 36 and the capabilities stated inthe MTR packet 126 it receives. It is noted that the term capabilitiesused throughout the present application includes the capabilities of themodems and of the lines of networks 34A or 34B as determined from thetraining.

In some embodiments of the invention, gateways 36A and 36B continue totransmit TRN signals 120 until they receive the MTR packet 126 from theother gateway. As the time required to demodulate MP signals 122 andtransmit MTR packets 126 is much shorter than the 2000 msec maximumtransmission time of TRN signals 120, the prolonged transmission of TRNsignals 120 does not violate the V.34 recommendation.

After phase 4 of the data pump (DP) negotiation is completed, modems 32Aand 32B optionally perform ECDC protocol negotiation and ECDC parameternegotiation. In some embodiments of the invention, gateways 36A and 36Bforward the ECDC negotiation signals they receive as if they are datasignals, as described hereinbelow, without relating to the contents ofthe signals. Thus, the ECDC negotiations are performed directly betweenmodems 32A and 32B and gateways 36A and 36B do not affect the contentsof the negotiation signals.

After the ECDC negotiation, modems 32A and 32B transmit to each otherdata signals at the rates set during the negotiation. In someembodiments of the invention, before beginning to transmit data and/orbefore the ECDC negotiation, gateways 36 transmit to each other dataphase negotiation (DPN) packets 132 notifying that data transmissionfollows. The data transmitted by modem 32A is received by modem 60Awhich transfers the data to IP interface 48A for transmission on UDPconnection 70. IP interface 48A packages the received signals intopackets. In some embodiments of the invention, the length of the datapayload of the packets is substantially equal to the processing blocksize of modems 60 of the gateway. For example, if the transmission rateis 28.8 Kbps and modem 60 processes blocks every 20 msec, the length ofthe data payload of the packets is 576 bits. In an embodiment of theinvention, if the number of data payload bits of a packet is notdivisible by eight, padding bits (e.g., ‘0’ bits) are added so that thepacket has an integer number of bytes.

In some embodiments of the invention, controller 46 (or any other unitof gateway 36A) examines the contents of the signals passed from modem60A to IP interface 48A to determine whether the signals includeinformation. Optionally, signals which do not include information, i.e.,signals which include filler sequences defined by modem recommendations,such as long sequences of ‘1’ bits or idle ECDC 7E signals, arediscarded and are not transmitted by interface 48A over UDP connection70. This behavior is referred to herein as V.42 idle flag blocking. Insome embodiments of the invention, controller 46 replaces the discardedsignals by control packets transmitted, for example, on TCP connection72 which state the number and/or nature of the discarded bits so thatgateway 36B can fill in the discarded signals. Alternatively, controlsignals are not transmitted instead of the discarded signals and gateway36B fills in the missing signals based on the rates of the modems inconnection 30. By discarding signals which do not carry information, theload on packet based network 38 is reduced allowing higher utilizationrates of the packet based network.

In some embodiments of the invention, the data packets transmitted by IPinterface 48A are delayed by jitter buffer 58B such that nearly all thesignals reach IP interface 48B after a fixed delay. In an embodiment ofthe invention, signals which do not reach IP interface 48B within thefixed delay are discarded and are considered lost in packet basednetwork 38. In some embodiments of the invention, the fixed delaycompelled by jitter buffer 58 is substantially the maximum delay whichdoes not cause the total delay between modems 32A and 32B to go beyondthe maximal delay allowed by the protocol governing the transmission onconnection 30. Alternatively, the fixed delay is set substantially inaccordance with any of the methods known in the art regarding VoIPand/or Fax over IP (FoIP). In some embodiments of the invention, thefixed delay compelled by jitter buffer 58 is set dynamically based onthe rate of packet loss in packet based network 38.

The signals in the data packets received by IP interface 48B are passedto modem 60B which transmits the signals to answer modem 32B. In someembodiments of the invention, when fewer signals than required for therate of transmission of connection 30 are received, gateway 36Bgenerates filler bits as defined in modem recommendations. In someembodiments of the invention, the filler bits are generated at leastpartially based on control packets transmitted from gateway 36A.

In some embodiments of the invention, the transmission of signals frommodem 32B to modem 32A is substantially as described above regarding thetransmission in the other direction. Alternatively, differenttransmission options are used for the different directions. For example,the discarding of signals may be performed in only one directionaccording to the load on packet based network 38.

In some embodiments of the invention, the data transmitted betweengateways 36 is encrypted in order to prevent eavesdroppers fromunderstanding the contents of the transmitted data. The encryption isespecially useful when packet based network 38 is not completelycontrolled by individuals who are obliged to adhere to high standards ofsecrecy.

In some embodiments of the invention, whenever a retrain, re-negotiateand/or terminate event occurs in one of the modem connections onswitched networks 34A or 34B, the gateway participating in the modemconnection in which the event occurred sends a notification packetidentifying the event to the other gateway. Responsive to thenotification packet, the other gateway initiates the same event in theother modem connection.

FIG. 5B is a time chart of the operations performed during are-negotiation event, in accordance with an embodiment of the presentinvention. When a re-negotiation is initiated by modem 32B, gateway 36Breceives the S, S signals 142 which signal the re-negotiation event inthe V.34 recommendation. Upon receiving S, S signals 142, gateway 36Btransmits a re-negotiation packet (PRN) 140 to gateway 36A, whichimmediately initiates a re-negotiation on its connection with modem 32A.The connections between modem 32A and gateway 36A and between modem 32Band gateway 36B both return to the beginning of phase 4, transmittingTRN messages 120 and 121 and then MP messages 122, as describedhereinabove.

The termination procedure of the V.34 recommendation includestransmitting MP signals which state zero rates. In some embodiments ofthe invention, the information in these MP signals is transmitted to theother gateway 36 in an MTR packet 126. Alternatively, as the informationin the MP signal is not required by the other gateway 36, a down signalpacket that merely indicates the termination event is sent to the othergateway.

FIGS. 6A and 6B are a time chart 200 of the operations performed duringthe second phase of a V.34 negotiation connection, in accordance withsome embodiments of the present invention. Generally, the methodillustrated by FIGS. 6A and 6B is performed by gateways 36 to causemodems 32A and 32B to determine round trip delay (RTD) valuescorresponding to the entire path between the modems, i.e., includingpacket based network 38. Modems 32A and 32B generally use the determinedRTD values in a time out mechanism of the error correction (EC) indetermining when to request a retrain. Thus, the method of FIGS. 6A and6B is generally used with gateways 36 which include modems 60 which donot perform error correction (EC), as shown in FIG. 3.

As shown in FIG. 6A, at the beginning of phase 2, call modem 32A and themodem of gateway 36B transmit INFO0c signals (202 and 204) one switchednetworks 34A and 34B, respectively. Likewise, answer modem 32B and themodem of gateway 36A transmit INFO0a signals (206 and 208) on therespective switched networks 34A and 34B. After completing thetransmission of INFO0c signal 202, modem 32A begins transmitting the Bsignal (210), which as all the other signals mentioned herein is definedin the V.34 protocol. When gateway 36A receives signal B 210, itoptionally checks if the recovery mechanism of the INFO signals 202 and208 was finalized. If the recovery mechanism was finalized, gateway 36Aresponds by transmitting signal A (212) on network 34A and in additiontransmits a notification packet (RB1) reporting the reception of signalB 210, to gateway 36B. Otherwise, gateway 36A waits for the recoverymechanism to be finalized before transmitting notification packet (RB1).Upon receiving packet RB1, gateway 36B begins transmitting signal B(214) on network 34B, if the recovery mechanism of the INFO signals 204and 206 was finalized. In some embodiments of the invention, if therecovery mechanism of the INFO signals 204 and 206 was not finalizedgateway 36B waits for the finalization before it transmits B signal 214.Alternatively, gateway 36B begins transmitting signal B (214) aftercompleting the transmission of INFO0c signal 204, irrespective of thereception of the RB1 packet. Optionally, in this alternative, the RB1packet is not transmitted. As is known in the art, modem 32B respondswith signal A (216) to the received signal B (214). After apredetermined time of at least 50 msec, modem 32B reverses the phase ofthe A signal 216 it transmits and thus transmits an Ā signal (218).Responsive to receiving the Ā signal 218, gateway 36B transmits an RĀ1packet to gateway 36A notifying that Ā signal 218 was received. Uponreceiving the RĀ1 notification packet, gateway 36A reverses the phase ofthe A signal 212 it is transmitting, thus transmitting an Ā signal 220.

As is defined by the V.34 protocol, 40 msec after receiving Ā signal 220modem 32A begins transmitting a B signal 222. When gateway 36A receivesB signal 222, it transmits a R B1 packet to gateway 36B, indicating thatB signal 222 was received. Responsive to the R B1 packet, gateway 36Btransits to modem 32B a B signal 224. When modem 32B receives B signal224 it responds to the received B signal 224 by waiting 40 msec andtransmitting A signal 226 for 10 msec, transmitting an L1 signal 228 for160 msec and then transmitting an L2 signal 230. In addition, modem 32Bcalculates a first round trip delay value (RTD) by subtracting 40 msecfrom the time T_(BAB) between when it transmitted Ā signal 218 and whenit received B signal 224. It is noted that gateway 36B does not respondwith B signal 224 40 msec after receiving Ā signal 218 but rather waitsuntil it receives the R B1 packet. Thus, the RTD calculated by modem 32Bcovers the entire round trip between modems 32B and 32A rather thanbetween modem 32B and gateway 36B.

In some embodiments of the invention, when gateway 36B receives A signal226 it does not reverse the phase of the B signal 224 it transmits, asprescribed by the V.34 recommendation, but rather continues to transmitB signal 224 without change. Instead, gateway 36B transmits to gateway36A an RA1 packet which indicates the reception of A signal 226. Whengateway 36A receives the RA1 packet, gateway 36A transmits to modem 32Aan A signal 232 for 10 msec, followed by an L1 signal 234 for 160 msecand an L2 signal 236.

In addition, modem 32A calculates a round trip delay value (RTD) bysubtracting 40 msec from the time T_(ABA) between when it transmitted Bsignal 222 and when it received A signal 232. It is noted that gateway36A does not respond with A signal 232 40 msec after receiving B signal222 but rather waits until it receives the RA1 packet. Thus, the RTDcalculated by modem 32A covers the entire round trip between modems 32Aand 32B rather than between modem 32A and gateway 36A.

Within 670 msec from receiving A signal 232, modem 32A transmits asecond B signal 240. In some embodiments of the invention, when gateway36A receives B signal 240, it transmits a RB2 packet which indicates thereception of B signal 240, to gateway 36B. Optionally, when gateway 36Breceives the RB2 packet it transmits a second B signal 242 to modem 32B.Alternatively, gateway 36B transmits the second B signal 242 accordingto its internal timing, independent of the reception of the RB2 packetwhich optionally is not transmitted. Further alternatively, whenpossible, i.e., less than 670 msec passed between receiving A signal 226and receiving the RB2 packet, B signal 242 is transmitted only after Bsignal 242 is received. If, however, it is not possible to wait thatlong, i.e., 670 msec passed since receiving A signal 226 and the RB2packet was not received, B signal 242 is transmitted without waiting forthe RB2 packet.

Turning to FIG. 6B, after B signal 242 is received by modem 32B, modem32B transmits a third A signal 244 for 50 msec, an Ā signal 246 for 10msec and then remains silent. In some embodiments of the invention, whengateway 36B receives A signal 244 it transmits a reception indicationpacket RA2 to gateway 36A. Optionally, gateway 36B additionallytransmits an RĀ2 packet (not shown), when it receives Ā signal 246.Responsive to receiving the RA2 packet, gateway 36A transmits an Asignal 248 for 50 msec, an Ā signal 250 for 10 msec and then remainssilent. As defined by the V.34 protocol, 40 msec after receiving Āsignal 250, modem 32A transmits a B signal 254 for 10 msec, an L1 signal256 for 160 ms and then transmits an L2 signal 258. Responsive toreceiving B signal 254, gateway 36A transmits a reception packet RB2packet to gateway 36B. Responsive to receiving reception packet R B2,gateway 36B transmits to modem 32B a B signal 260 for 10 msec, an L1signal 262 for 160 msec and an L2 signal 264. In addition, modem 32Bcalculates a second RTD value by subtracting 40 msec from the timeT_(BAB2) between when it transmitted Ā signal 246 and when it received Bsignal 260.

Within 670 msec from receiving B signal 260, modem 32B transmits afourth A signal 266 to gateway 36B. Responsive to receiving B signal260, gateway 36B transmits a reception packet RĀ3 to gateway 36A whichin turn transmits an A signal 268 to modem 32A. Alternatively, packetRA3 is not transmitted and/or A signal 268 is transmitted independent ofthe time at which A signal 266 is transmitted. In an exemplaryembodiment of the invention, A signal 268 is transmitted by gateway 36Aa predetermined number of msec after receiving L2 signal 258. Thepredetermined number of msec may be a fixed number, for example between300-500 msec or may be a function of the round trip delay (RTD) ofsignals on network 38. Optionally, gateway 36A determines the RTD ofsignals on network 38 by subtracting a correction factor from the timebetween transmitting the R B1 packet and receiving the RA1 packet. Thecorrection factor is possibly equal to 40 msec added to an estimate ofthe RTD of signals on switched networks 34.

Further alternatively, A signal 268 is transmitted within the required670 msec of the V.34 protocol, if possible after receiving the RA3packet.

Responsive to A signal 268, modem 32A transmits, to gateway 36A, anINFO1c signal 270 as required by the V.34 protocol. Responsive to INFO1csignal 270, gateway 36A transmits a reception packet RINFO1c, whichindicates the reception of INFO1c signal 270 to gateway 36B. In thisembodiment, the reception packet RINFO1c does not include the data ofINFO1c signal 270. Responsive to reception packet RINFO1c, gateway 36Btransmits to modem 32B an INFO1c signal 272. As required by the V.34protocol, modem 32B responds to INFO1c signal 272 with an INFO1a signal274. Responsive to INFO1a signal 274, gateway 36B transmits a receptionpacket INFO1a to gateway 36A. Responsive to reception packet RINFO1a,gateway 36A transmits to modem 32A an INFO1a signal 276.

Alternatively, gateway 36A responds to INFO_(1c) signal 270 with INFO1asignal 276 substantially immediately, i.e., without relation to thetiming of the signals on network 34B. In this alternative, the RINFO1cand RINFO1a packets are optionally not transmitted.

Further alternatively, the RINFO1c packet includes at least some of thedata in INFO1c signal 270 and/or the RINFO1a packet includes at leastsome of the data in INFO1a signal 274. In some embodiments of theinvention, the contents of the RINFO1c packet are used in generatingNFO1c signal 272 and/or the contents of the RINFO1a packet are used ingenerating INFO1a signal 276. For example, the RINFO1a packet mayinclude the symbol rate used on network 34B and gateway 36 a uses theinformation from the RINFO1a packet to make sure, if possible, that thesymbol rates on networks 34A and 34B are equal.

In some embodiments of the invention, the above described receptionnotification packets (e.g., RA1, RA2, RA3, RĀ1, RĀ2, RB1, RB2, R B1, RB2, RINFO1c and RINFO1a) transmitted on packet based network 38, may bein substantially any format, for example in a format similar to thedefinitions of packets in the T.38 recommendation. In some embodimentsof the invention, some or all of the reception notification packets,particularly those which are required for time measurements, aretransmitted a multiplicity of times to reduce the chances of problemsdue to packet loss. In some embodiments of the invention, the number oftimes each reception notification packet is transmitted is determined asa function of the loss rate of network 38, such that the chances thatall the copies of a specific packet will be lost is beneath apredetermined value.

In some embodiments of the invention in which gateways 36A and/or 36Bapply a buffer delay T_(jitter) for jitter prevention to data signalsthey receive, the same delay T_(jitter) is applied also to the receptionnotification packets. Alternatively the T_(jitter) delay is applied onlyto reception notification packets which are involved in a transmissionpath whose time is measured, e.g., RĀ1 and R B1. Alternatively todelaying the reception notification packets, gateways 36A and/or 36Bwait a time T_(jitter) between receiving the reception notificationpackets and transmitting respective switched network signals (forexample, Ā signal 220, B signal 224) which are transmitted responsive toreceiving the packets.

Alternatively to using the procedure of FIG. 6 which requirestransmission of reception indication packets between gateways 36A and36B, each of gateways 36A and 36B delays the transmission of timingsignals for an estimated delay period in addition to the delay periodprescribed by the relevant protocol, e.g., 40 msec in the V.34. In someembodiments of the invention, the delay period comprises a sum of theround trip delay of network 38 and of an estimate of the delay period ofthe remote switched network, i.e., the network 34A or 34B to which thegateway is not directly connected.

In some embodiments of the invention, before and/or at the beginning ofphase 2, the round trip delay of packets on the network 38 included inthe current MoIP connection 30, is measured. Optionally, the round tripdelay is measured by transmitting an echo request packet (e.g., an ICMPecho request) from one of the gateways 36 to the other and measuring thetime between transmitting the echo request and receiving the responsethereto, from the other gateway. Alternatively or additionally, each ofgateways 36A and 36B transmits to the other gateway a packet including atime stamp. The round trip delay of network 38 is then calculated astwice the difference between the reception time and the time stamp inthe packet. In some embodiments of the invention, the round trip delayis measured a few times and the highest value is used. Alternatively oradditionally, a safety margin is added to the measured RTD value ofnetwork 38. Further alternatively or additionally, the RTD of network 38is kept substantially constant for any specific MoIP connection 30, forexample by using jitter buffers and/or by using load regulated packetbased networks.

In some embodiments of the invention, gateways 36A and/or 36B use apredetermined value for the estimate of the round trip delay (RTD) ofall remote switched networks. It is noted that most MoIP connectionsinclude relatively short switched network segments. Furthermore, in mostMoIP connections the delay of the switched networks is small relative tothe delay of the packet based network 38. Therefore, inaccuracies in theestimate of the round trip delay of the remote switched network 34 areunimportant. Optionally, the estimate of the RTD of remote switchednetworks is configured by a network manager. Alternatively oradditionally, the estimate of the RTD of remote switched networks isperiodically determined by gateways 36A and 36B based on periodicmeasurements. In some embodiments of the invention, the estimate of theRTD of remote switched networks is set as an upper bound on the RTD ofswitched networks. Alternatively, the average value of the RTD ofswitched networks, is used.

It is noted that in the absence of far echo effects, as is generally thecase in MoIP connections (due to the relatively short distance betweenmodem pairs 32A and 60A and 32B and 60B) incorrect RTD values do notcause distortions, as no echo cancellation is actually performed.Although the above method for adjusting the measured RTD was describedwith relation to the V.34 protocol, the above method may be implementedfor substantially any other voice band modem protocol. Optionally, inprotocols which do not measure the RTD, e.g., the V.22 protocol,gateways 36A and 36B cause modems 32A and 32B to use time-out valueswhich take into account worst case times of MoIP connections.

FIG. 7 is a schematic block diagram of gateways 36A and 36B and theconnections between them, in accordance with another embodiment of thepresent invention. In the embodiment of FIG. 7, gateways 36A and 36Binclude IP interfaces 48 and controllers 46 similar to that describedabove with respect to FIGS. 2 and 3, but include modems 300 whichinclude error correction (EC) units 43 but do not perform datacompression (DC) termination. Instead, the DC termination is performeddirectly between call and answer modems 32A and 32B.

Not providing DC termination by gateways 36 simplifies modems 300 andreduces their power and memory consumption. It is noted that modem 300may be part of a modem array. By not performing DC by modem 300, thenumber of connections handled by the modem array may be substantiallylarger than if DC termination is performed.

In some embodiments of the invention, IP interfaces 48A and 48Bcommunicate over a connection of a delivery confirming protocol, such asover a TCP connection 50 established within packet based network 38. Theuse of a delivery confirming protocol prevents occurrence of problems indecompression due to loss of data on packet based network 38.Alternatively, a non delivery confirming protocol (e.g., UDP) is used,optionally with forward error correction methods which reduce thechances of errors occurring in the received signals.

In some of the embodiments of the invention in accordance with FIG. 7,the connections on switched networks 34A and 34B may be in accordancewith different protocols, rates and/or other parameters. In theseembodiments, gateways 36A and 36B do not mirror to each other controlsignals during one or more negotiation stages of the connections. Thus,the selection of protocols, symbol rates and/or data rates is performedindependently for each of switched networks 34A and 34B.

Alternatively, one or more parameters of the connections on switchednetworks 34A and 34B are correlated, for example using any of themethods described above, in order to minimize the time differencebetween transmitting the same signals, particularly negotiation signals,on switched networks 34A and 34B. For example, in some embodiments ofthe invention, the signals of the first phase of the negotiation stage(e.g., the V.8 phase) are mirrored between gateways 36A and 36B asdescribed above with reference to FIG. 4, so that the connections onboth networks 34A and 34B follow the same protocol. Having theconnections on networks 34A and 34B follow the same protocol limits thetime difference between the entering of the data transmission stage onboth of networks 34A and 34B.

In some embodiments of the invention, also negotiation signals offurther negotiation stages are correlated as described hereinabove withreference to FIGS. 5A and 5B, in order to further limit the timedifference between the entering of the data transmission stage on bothof networks 34A and 34B. Alternatively, the timing of the signals duringone or more of the negotiation stages is correlated without correlatingthe contents of the signals.

In some embodiments of the invention, as described, for example, withreference to FIG. 8, ECDC parameter negotiation signals transmitted atthe beginning of the data transmission stages are mirrored by gateways36A and 36B to each other, such that the compression negotiation isperformed between modems 32A and 32B.

FIG. 8 is a time chart of the frames transmitted between modems 32A and32B during an ECDC parameter negotiation stage, in accordance with someembodiments of the present invention. As is known in the art, when theconnections between modem 32A and gateway 36A and gateway 36B and modem32B are established, the modems and gateways perform data pump (DP)training stages 306 (e.g., phases 1-4 of the V.34 recommendation) andthen perform an ECDC protocol negotiation stage 308 (e.g., selecting MNPor V.42). DP training stages 306 and protocol negotiation stage 308 maybe performed on the connections of networks 34A and 34B separatelywithout exchanging information between gateways 36A and 36B or withpartial or complete correlation between the connections, for example asdescribed above with reference to FIGS. 5A and 5B, regarding DP stages306.

After completing data pump training 306 and ECDC protocol negotiationstage 308, the connections on switched networks 34A and 34B move to anECDC parameter negotiation stage 309, governed by the protocol selectedduring the ECDC protocol negotiation 308. It is noted that thecompression negotiation stage on networks 34A and 34B are notnecessarily governed by the same protocol. Alternatively, gateways 36Aand 36B correlate the signals transmitted during ECDC protocolnegotiation stage 308 to force both the connections on networks 34A and34B to select the same ECDC protocol, for example using methods similarto those described above to force the connections to choose the same DPprotocol during phase-1.

As is known in the art, at the beginning of ECDC parameter negotiationstage 309, call modem 32A transmits a caller-compression capabilityframe 310 (e.g., an XID or LR frame) to gateway 36A. Optionally, insteadof responding immediately on switched network 34A, gateway 36A transmitsa caller compression capability packet 312 containing the data of frame310 to gateway 36B, and waits for a response thereto before respondingto frame 310. After a time-out interval T₄₀₁ call modem 32A may repeatthe transmission of its frame 310. Optionally, gateway 36A will continuenot to respond to the frame 310. Alternatively, gateway 36A responds(not shown) to the first frame 310, or to the repeated frame 310, withguess values, as described hereinbelow.

In some embodiments of the invention, when gateway 36B receives packet312 it transmits a caller compression capability frame 314 to modem 32B.Optionally, the contents of compression capability frame 314 depend onthe contents of packet 312, as described hereinbelow. In someembodiments of the invention, DC related information in frame 314 issubstantially identical to the respective information in frame 310 whichcaused the transmission of packet 312. When modem 32B receives frame 314it responds with an answer compression capability frame 316 whichidentifies the compression parameters of modem 32B. Upon receiving frame316, gateway 36B transmits an answer compression capability packet 318including the contents of frame 316 to gateway 36A. In addition, gateway36B responds to modem 32B with a response frame 320 (e.g., a SABME frameor an LA frame) according to the compression protocol in use. Inaccordance with some protocols, e.g., the V.42 protocol, modem 32Bresponds with a response confirmation frame 321 (e.g., a UA frame).

Responsive to receiving answer compression packet 318, gateway 36Aoptionally transmits an answer compression frame 322 to modem 32A whichidentifies the compression capabilities of modem 32B, as identified byframe 316 and transferred by packet 318. As is known in the art, modem32A responds to compression frame 322 with a response frame 324 (e.g., aSABME frame or an LA frame). In accordance with some protocols, gateway36A responds with a response confirmation frame 326 (e.g., a UA frame).

It is noted that frames 310 and 316 may include also EC relatedinformation. Optionally, the EC related information is not transferredin packets 312 and 318 between gateways 36A and 36B and/or does notaffect the contents of frames 314 and 322. Alternatively, in someembodiments in which the EC layers of the connections on networks 34Aand 34B are correlated some and/or all of the parameters in frames 310and 316 are transferred between gateways 36A and 36B.

Thereafter, modems 32A and 32B transmit to each other data. Data signalsreceived by gateways 36A and 36B are optionally forwarded to the othergateway in data packets, on a TCP connection 50 (FIG. 7). In someembodiments of the invention, when the flow control (e.g. window size)of TCP connection 50 does not allow transmission of all the datareceived by a gateway 36 through its modem 300, the gateway 36 (36A or36B) optionally uses modem flow control methods (e.g., not transmittingacknowledgments) to stop the transmission of data to the gateway overthe switched network 34 to which it is connected. Alternatively oradditionally, the gateway 36 buffers the data it receives on network 34until the data may be transmitted on TCP connection 50. When one of theconnections on networks 34A and 34B is closed, the gateway 36 attachedto the closed connection closes the TCP connection 50 and thus signalsto the other gateway 36 to close its modem connection.

In some embodiments of the invention, when during transmission of data abreak frame (e.g., a UI frame of the V.42 protocol or an LN frame of theMNP protocol) is received from one of end modems 32A or 32B, the gateway36 receiving the break frame notifies the other gateway in addition toresponding to the break frame as required by the protocol used. Gateways36 optionally notify each other on reception of a break frame bytransmitting a break packet which states the reception of the breakframe, the type of the break (e.g., destructive, expedited), anattention sequence number and possibly includes a break length.Optionally, a break length is included in the break packet if thereceived break frame included a break length field. Alternatively oradditionally, a break length is included in the break frame only if theconnections on both networks 34A and 34B support the indication of breaklengths in their break frames. The gateway receiving the break packettransmits a respective break frame on its modem connection.

Referring in more detail to the contents of caller compressioncapability frame 314, in some embodiments of the invention, when gateway36B knows that modem 32B operates in accordance with a differentcompression protocol than modem 32A, the contents of frame 314 indicatethat modem 32A does not support compression. When gateway 36B is notaware of whether modem 32A and 32B use different protocols or whengateway 36B knows that both modems use the same compression protocol,the contents of frame 314 optionally follow the contents of packet 312.

Alternatively or additionally, when gateway 36B knows that modem 321operates in accordance with a different compression protocol than modem32A, gateway 36B immediately responds to packet 312 by transmittingpacket 318 with indication of no compression, without waiting forreception of frame 316.

Further alternatively or additionally, gateways 36A and 36B exchangepackets indicating the protocols selected in ECDC protocol negotiation308 before beginning ECDC parameter negotiation 309. Optionally, if theprotocols used on the connections of networks 34A and 34B are different,ECDC parameter negotiation 309 is performed independently on connections34A and 34B (i.e., packets 312 are not exchanged between gateways 36Aand 36B).

FIGS. 9A, 9B and 9C describe three exemplary scenarios of ECDC parameternegotiation, in accordance with some embodiments of the presentinvention. In FIG. 9A, both switched network connections select V.42during ECDC protocol negotiation 308. Frame 310 indicates that modem 32Ahas V.42 compression capabilities and frame 314 indicates the same.Modem 32B responds with frame 316 which indicates V.42 compressioncapabilities and therefore the data transmitted between modems 32A and32B is compressed in accordance with the V.42 protocol.

In FIG. 9B, the connection on switched network 34A selects the V.42protocol and the connection on switched network 34B selects the MNPprotocol during ECDC protocol negotiation 308. In ECDC parameternegotiation 309, modem 32A indicates in frame 310 that it supportscompression. However, when gateway 36B receives packet 312 whichindicates V.42 compression which is different from the MNP compressionused on the connection with modem 32B, it indicates no compressionsupport to answer modem 32B. Therefore, the data transmitted betweenmodems 32A and 32B is not compressed.

In FIG. 9C, both switched network connections select V.42 during ECDCprotocol negotiation 308. In ECDC parameter negotiation 309, modem 32Aindicates in frame 310 that it supports compression and this informationis forwarded to modem 32B in frame 314. Answer modem 32B, however, doesnot support compression and therefore the data transmitted betweenmodems 32A and 32B is not compressed.

In some embodiments of the invention, when gateway 36B knows that modem321 does not support compression or does not support the compressionmethods supported by modem 32A, gateway 36B does not wait for receivingpacket 312 in order to transmit frame 314. Instead, gateway 36Btransmits frame 314 immediately when it finishes phase 4 of thenegotiation stage. Thus, the time required for compression negotiationis reduced.

In some embodiments of the invention, when more than a predeterminedtime passes between the end of the connection establishment negotiationstage on network 34B and gateway 36B did not yet receive packet 312,gateway 36B repeatedly transmits frame 314 with guess values (orpredetermined values) until packet 312 is received, in order to preventmodem 32B from disconnecting the connection due to the long silenceinterval. As is known in the art, modem 32B will respond with frames 316to each frame 314 transmitted by gateway 36B. Gateway 36B does notrespond to these frames 316 with response frame 320 and does nottransmit packets 318 responsive to these frames 316.

In some embodiments of the invention, when gateway 36B finally receivespacket 312, it transmits a frame 314 with values taken from packet 312.When gateway 36B receives a frame 316 generated responsive to this frame314, it transmits packet 318 to gateway 36A and transmits response frame320 to modem 32B. Optionally, if the values in the received packet 312are equal to the guess values in repeatedly transmitted frames 314,gateway 36B transmits response frame 320 and packet 318 responsive toreceiving packet 312.

When gateway 36B receives packet 312 before the connection establishmentnegotiation stage on network 34B is completed, gateway 36B optionallywaits to the end of the negotiation stage before transmitting frame 314.In some embodiments of the invention, Gateway 36B reports the delay togateway 36A in a suitable packet, and gateway 36A repeatedly transmitsframes 322 with guess values to modem 32A, in order to stall theconnection on network 34A. As is known in the art, modem 32A responds torepeatedly transmitted frames 322 with response frames 324. It is noted,however, that since gateway 36A does not confirm the receipt of responseframes 324, the connection on network 34A does not proceed.

Optionally, when compression packet 318 is received from gateway 36B,gateway 36A transmits an answer compression capability frame 322 withvalues taken from the received packet 318. When modem 32A responds witha response frame 324, gateway 32A confirms receipt of the frame 324 bytransmitting frame 326 and the connection moves to data transmission. Insome embodiments of the invention, if the guess values of repeatedlytransmitted frames 322 are equal to the values in packet 318, gateway36A transmits confirmation frame 326 immediately when packet 318 isreceived.

Alternatively or additionally to gateway 36B transmitting to gateway 36Aa packet which reports the delay due to network 34B being still in theconnection establishment negotiation stage, gateway 36A beginstransmitting frames 322 with guess values after a predetermined time inwhich packet 318 was not received.

In some embodiments of the invention, the guess values used inrepeatedly transmitted frames 314 and/or 322 are selected randomlyand/or are configured at manufacture or installment of gateway 36Band/or 36A. Alternatively or additionally, the guess values used inrepeatedly transmitted frames 314 and/or 322 are selected responsive toone or more parameter values exchanged or determined during thenegotiation stage of the connection (e.g., the quality of networks 34Aand/or 34B) and/or responsive to one or more parameters of the formationof the connection (e.g., the telephone number). Further alternatively oradditionally, the guess values used in repeatedly transmitted frames 314and/or 322 are selected based on actual values received in recentlyestablished connection, optionally of previous connections having commoncharacteristics. Further alternatively or additionally, the guess valuesindicate the maximal possible compression capabilities.

In some embodiments of the invention, packets 312 and 318 have astructure similar to any of the structures described above, and/orsimilar to that described in the T.38 ITU recommendation. In anexemplary embodiment of the present invention, each packet has a typeheader which identifies the packet and a content field which carries theremaining portion of the packet. Optionally, the type header identifieswhether the packet carries data, a disconnect instruction, and/or acompression capability packet. Possibly, packets which indicate nosupport of compression have a different type value than packets whichindicate support of compression. Optionally the content field has aninternal length field which indicates the length of the data.Alternatively or additionally, one or more external headers (e.g., TCP,IP) indicate the length of the data in the content field. Optionally,packets which indicate no support of compression do not contain acontent field.

In some embodiments of the invention, gateways 36A and 36B includemodems which perform data pump (DP) and the HDLC tasks of the EC tasksand do not perform the DC tasks and the remaining tasks of the EC tasks.Data signals received from modems 32A and 32B by gateways 36A and 36B,respectively, are demodulated by the gateways. Padding flags and the CRCfield are removed, by gateways 36A and 36B, from the demodulated databits, and erroneous frames are discarded. The resulting frames areencapsulated and forwarded to the other gateway (without loss ofgenerality 36B), using any of the encapsulation methods described above.The receiving gateway 36B acknowledges the receipt of the flames(optionally within frames of data signals transmitted to gateway 36A)and exchanges flow control commands (e.g., retransmission requests,buffer full notices) with gateway 36A. Gateway 36B also removes theencapsulation, performs flag padding, adds a CRC, modulates the signalsand transmits them to modem 32B.

Gateways 36A and 36B exchange DP control signals with modems 32A and 32Brespectively, in accordance with any of the methods described above.Optionally, delay procedures as described above with reference to FIGS.6A and 6B are used during the stage in which the round trip delay ismeasured. In addition, HDLC control signals are generated and handled bygateways 36A and 36B locally with their respective modems 32A and 32B.On the other hand, LAPM and DC control signals are forwarded by gateways36 as data signals, with or without being aware of their being controlsignals.

It is noted that a single gateway 36 may support a plurality of thedifferent embodiments described above. For example, a gateway mayoperate without performing error correction (EC) and data compression(DC) for a first group of connections or at a first time (e.g., duringwork hours), while for other connections or at other times the gatewayoperates with performing EC and optionally also DC. In some embodimentsof the invention, when a connection is established, gateways 36A and 36Bnegotiate with each other over network 38 the specific embodiment theyare to use.

In some embodiments of the invention, gateways 36A and 36B determinewhether to act in accordance with one of the MoIP methods describedabove, and/or according to which of the above MoIP methods to act,responsive to the contents of the signals transmitted at the beginningof the connection.

FIG. 10 is a flowchart of the acts performed by a gateway 36 uponestablishing a connection, in accordance with an embodiment of thepresent invention. When a new connection is established (400) throughgateway 36, the gateway operates in a VoIP state (404), for example asdescribed in the G711 ITU recommendation. In the VoIP state (404)(referred to also as MoIP type 0), signals received from switchednetworks 34 are converted into packets and are transmitted over packetbased network 38 without performing demodulation. In addition, signalsreceived from packet based network 38 are extracted from their packetsand are transmitted on switched network 34, without performingmodulation of the signals. Optionally, upon establishment of theconnection, the gateway transmits negotiation signals over packet basednetwork 38 to the remote gateway 36 which takes part in the establishedconnection. If the remote gateway 36 responds to the negotiationsignals, a MoIP negotiation procedure (402) is performed, as describedhereinbelow, to determine which MoIP method to use if the connectioncarries modem signals.

If (406), during transfer of signals, gateway 36 identifies a dataidentification signal (e.g., a 2100 Hz signal), gateway 36 disables echocancellation and VAD/CNG (voice activity detection) (408), as is knownin the art. In some embodiments of the invention, gateway 36 also beginsto listen (410) to the transferred signals in order to determine whethera Fax or modem handling method other than VoIP state (404) is required.If (420) the transferred signals comprise signals of a specific protocolsupported by gateway 36, and optionally also by the remote gateway 36,e.g., T.30 flags, gateway 36 moves immediately to a handling state (422)of the specific protocol (e.g., for T.30 flags, as prescribed by theT.38 recommendation). In some embodiments of the invention, if (412) thetransferred signals are according to a protocol negotiation procedure(e.g., the V.8 procedure) supported by gateway 36, and optionally alsoby the remote gateway 36, gateway 36 does not move immediately to a MoIPmethod as described, for example, with reference to FIG. 4 above.Instead, gateway 36 continues to operate in VoIP state (404), such thatthe V.8 negotiation is performed between the end modems 32 (FIG. 1), butbegins to decipher the transferred signals (424), i.e., determines thebit content of the signals. Gateway 36 optionally deciphers thetransmitted signals so as to determine the protocol which will governthe transmission of data signals on the connection.

If (426) the determined protocol for data transmission is supported bygateway 36, and optionally also by the remote gateway 36 (as determinedin negotiation 402), gateway 36 selects (414) a handling method (whichincludes performing modulation and demodulation) to be used for the datatransmission protocol. In some embodiments of the invention, thehandling method is selected also responsive to other deciphered signals(e.g., the transmission rate of the connection) and/or responsive toresults of the previously performed negotiation procedure (402). In anexemplary embodiment of the invention, gateway 36 selects a handlingmethod for the V.34 (full duplex), V.90, V.91 and V.92 protocols fromone of the MoIP handling methods described above. Alternatively, themovement to a MoIP state may be performed for other groups of protocols.

If the signals on the connection are not in accordance with a protocolsupported by gateway 36 (or optionally the remote gateway 36), or theprotocol determined to be used for data transfer is not supported bygateway 36 (or optionally the remote gateway 36), gateway 36 continuesto operate in the VoIP state (404). It is noted that if the data signalsare transmitted at a very low rate, the signals may pass on theconnection at a tolerable quality even though VoIP state 404 is used.

In some embodiments of the invention, selecting (414) the handlingmethod includes selecting a predetermined transfer point in whichgateway 36 moves from VoIP state (404) to the selected handling (MOIP)method. In some embodiments of the invention, for the V.34, V.90, V.91or V.92 protocols, the transfer time is after the end of the V.8negotiation, i.e., after the CJ signals, in the recess between phase 1and phase 2 of the protocol negotiation procedure. The end of the V.8negotiation is optionally used as the transfer point, since there is aninterval in which no signals are transmitted on the connection betweenthe end of the V.8 negotiation and the beginning of phase 2 negotiationin accordance with the selected protocol.

Alternatively or additionally, the transfer point is selected as anyother sufficiently long recess in which the change of handling will notcause ambiguities on the connection. For example, in some embodiments ofthe invention, the transfer point is after the second phase ofnegotiation, such that the symbol rate is determined directly betweenthe end modems 32. Thus, there is no need to perform symbol ratespoofing and/or RTD time correction (as described above with referenceto FIGS. 6A and 6B). It is noted, however, that earlier transfer to theselected MoIP method is preferred, as transmission of modem signals inVoIP state (404) may suffer from quality degradation due to packet basednetwork 38.

Gateway 36 optionally continues to decipher the signals passing on theconnection until the transfer point is identified (416). Thereafter,gateway 36 begins to operate (418) in accordance with the selected MoIPmethod, i.e., begins to perform modulation and demodulation on thesignals it forwards. In some embodiments of the invention, the movement(418) to the MoIP method is performed without notifying the remotegateway 36 and/or waiting for confirmation from the remote gateway 36.Rather, the transfer is performed based on the previously performednegotiation (402) and/or predetermined rules set before the connectionwas established. Thus, the mode transfer may be performed fast enough toadhere to the time constraints of the protocol governing the connection.Alternatively, the formation of a control IP connection is used todetermine whether the remote gateway 36 supports MoIP. If the remotegateway 36 accepts the establishment of the connection, it supportsMoIP, otherwise it is known that the remote gateway 36 does not supportMoIP.

Referring in more detail to performing the negotiation (402), gateway 36optionally transmits to the remote gateway a list of the protocols itsupports and the MoIP methods it may use with each protocol. In someembodiments of the invention, gateway 36 receives a similar list fromthe remote gateway 36. Each of the gateways 36 optionally generates aconnection list which includes the common elements of the lists. Whenthe common list includes more than one MoIP method for a protocol, themethod to be used is selected according to predetermined rules. Forexample, the different MoIP methods may be ordered in a preferenceorder, e.g., always prefer MoIP in which gateways 36 perform EC overMoIP in which gateways 36 perform ECDC. The preference order may begeneral for all protocols or may be different for different protocols.Alternatively or additionally, the predetermined rules for selecting theMoIP method may depend on one or more parameters of the connection, suchas the bit rate. For example, for slow bit rates a first MoIP method maybe preferred while for fast bit rates a second MoIP method is preferred.

In some embodiments of the invention, the lists transmitted during thenegotiation (402) include, for each protocol, one or more suitabletransfer points. Optionally, a predetermined rule is used to determinewhich transfer point to use when there are a plurality of possibletransfer points. The rule for determining the transfer point optionallychooses the earliest or latest possible transfer point or sets apreference order.

Alternatively to negotiation (402) including transmission of a list,negotiation (402) includes transmission, by each of gateways 36 to theother gateway 36, of a gateway type message. Optionally, each gateway 36includes a list of the capabilities of each type of gateway, such thataccording to the gateway type message the types of protocols supportedby the remote gateway 36 are known. The type message may include a modeltype, a model date which indicates operation with all model types frombefore the date and/or a simple message of MoIP support.

In some embodiments of the invention, the negotiation (402) includes ahandshake procedure, optionally a double handshake procedure, whichensures that both gateways 36 receive the list from the other gateway36. In some embodiments of the invention, if the handshake is notcompleted within a predetermined amount of time from the beginning ofthe connection or until a predetermined decision point which depends onthe signals passing on the connection, VoIP state (404) is used.Optionally, the predetermined amount of time or the predetermineddecision point are selected such that the decision as to whether thehandshake was successful occurs before the first possible transferpoint. Alternatively, the predetermined amount of time or thepredetermined decision point are selected such that the decision ofwhether the handshake was successful occurs before the last possibletransfer point. In some embodiments of the invention, the selection ofthe transfer point depends on the time at which the handshake wascompleted.

In some embodiments of the invention, as shown in FIG. 10, negotiation(402) is performed before gateway 36 knows whether the connection is adata connection. Alternatively, negotiation (402) begins only after thedata identification signal is identified. Further alternatively, thenegotiation (402) begins only after the specific protocol passing overthe connection is identified. In some embodiments of the invention, ifthe negotiation (402) does not end successfully on time, gateway 36 usesspoofing methods in order to stall the connection until the negotiationis completed.

In some embodiments of the invention, negotiation (402) is notperformed, for example when it is clear that the remote gateway 36 hassubstantially the same capabilities as the determining gateway 36 orwhen there is substantially no chance of successful transmission if theremote gateway 36 does not support MoIP.

Alternatively or additionally to using the method of FIG. 10, differentdata identification signals are used by end users for different types ofdata connections. For example, slow Fax data connections, and other dataconnections which do not require MoIP handling, may use a firstidentification signal and additional unique signals are used by otherprotocols according to the type of MoIP they are to use. Responsive tothe data identification signal transmitted on the connection, gateway 36optionally selects the MoIP method to be used (if at all). Thus, gateway36 may operate for a plurality of different types of connections andstill begin its MoIP handling before V.8 negotiation, for example,begins.

Further alternatively or additionally, other identification methods maybe used, such as separate telephone numbers for different types ofconnections and/or any of the methods described in PCT applicationPCT/IL00/00288 titled “Back to Back Modem Repeater”, the disclosure ofwhich is incorporated herein by reference.

Further alternatively or additionally, when gateway 36 identifies thebeginning of a V.8 procedure, i.e., an ANSam signal, gateway 36 moves toa MoIP method, as described above with reference to FIG. 4. If duringthe MoIP handling of the V.8 procedure it is determined that the dataprotocol is not supported by gateway 36 or by remote gateway 36, gateway36 moves back to VoIP state 404 at the end of the V.8 procedure. In someembodiments of the invention, provisions are taken as described above,to ensure that both of the connections on switched links 34 move back toVoIP state 404 at substantially the same time.

In some embodiments of the invention, the MoIP connections describedabove are implemented by a telephone service provider with or withoutthe knowledge of the users. It is noted that the total delay of MoIPconnections is accordance with the present invention are between about100-300 msec, and therefore the delay is not generally identified byusers of modems. In some embodiments of the invention, gateways 36A and36B are included in central offices (COs), digital loop carriers (DLC)and/or any other elements of a telephone network. Optionally, gateways36A and 36B are in the COs which generally service the telephone linesto which the modems 32A and 32B are connected. Alternatively oradditionally, gateways 36 are included in remote access servers (RASs)and/or Remote access communicators (RACs) of an Internet serviceprovider.

In some embodiments of the invention, the MoIP connections describedabove are managed by a packet based network maintainer in order toprovide alternative communication services. For example, instead ofcalling a target modem in an expensive long distance call, a client maycall a local gateway, which forms a packet base connection with a remotegateway in the vicinity of the target modem and a modem connection fromthe remote gateway to the target modem. In some embodiments of theinvention, Internet service providers (ISPs) may provide in addition tostandard Internet access, modem access services, which allow securetransmission of signals to a remote modem.

Although in the above description gateways 36A and 36B are connectedthrough a packet based connection, the present invention is not limitedto transmission of VBM signals over packet based networks. Rather, themethods described above may be employed when gateways 36A and 36B areconnected through other types of network paths, including analog lines,digital paths (e.g., digital circuit multiplication equipment (DCME),SONET) and combinations thereof. It is noted, however, that such othertypes of network paths may have shorter round trip delays and shorter orno jitter and therefore may not require some of the above describedmethods in order to allow transmission of modem signals on the networkpaths between gateways 36A and 36B.

In some embodiments of the invention, the network path between gateways36A and 36B is part of a multi-point network which connects a pluralityof gateways and/or other communication units. Optionally, the network towhich the path between gateways 36A and 36B belongs is an addressablenetwork (i.e., a non-dedicated network) in which signals may be sentfrom a source to one or more of a plurality of destinations.Alternatively, the network path between gateways 36A and 36B is adedicated link. Optionally, when a dedicated link is used, addressingheaders are not required and/or some or all of the negotiationprocedures are not required as the parties to the connection arepredetermined.

In some embodiments of the invention, gateways 36A and 36B or variantsthereof are used for other purposes than the formation of a MoIPconnection. For example, as is now described with reference to FIGS.11-13, a pair of interconnected modems are used, in some embodiments ofthe invention, as a repeater which allows use of high-speed modemconnections over a pair-gain system. In other embodiments of theinvention, as described for example with reference to FIGS. 14-16 belowand/or in Israel patent application 141,753 filed Mar. 1, 2001, thedisclosure of which is incorporated herein by reference, a distributedremote access (RAS) comprises two or more parts, optionally in differentlocations, one of which parts is similar to gateway 36.

FIG. 11 schematically shows a pair-gain system 580 that can support fastmodem transmissions (e.g., according to V.90, V.91, V.92), in accordancewith an embodiment of the present invention. Pair gain system 580comprises a central office terminal 534 which connects to a centraloffice (CO) 522 over a plurality of twisted pairs 542, and a remoteterminal 536 which connects to a plurality of customers (e.g.,hand-sets, modems) 524 over twisted pairs 540. Central office terminal534 and remote terminal 536 are connected through a twisted pair 538 onwhich high speed modems 560 and 568 of terminals 534 and 536,respectively, transmit to each other signals they receive on theirtwisted pairs 540 and 542. Thus, a single twisted pair 538 is usedinstead of a plurality of twisted pairs, due to the high transmissionspeeds of modems 560 and 568.

In some embodiments of the invention, in order to prevent qualitydegradation of signals transmitted from CO 522 to customers 524repeaters 582, as described hereinbelow, are included in pair-gainsystem 580. It is noted that substantially all the other elements ofpair gain system 580 are as is known in the art, such that, in someembodiments of the invention, upgrading a pair gain system to supportfast modem transmissions (e.g., above 33,600 bps), requires only theaddition of repeaters 582. Optionally, repeaters 582 connect to highspeed modem 560 through a multiplexer 562.

FIG. 12 schematically shows pair-gain system 580 and details of onerepeater 582, for servicing V.90 fast modem calls, comprised in itscentral office terminal 534, in accordance with an embodiment of thepresent invention. Features not germane to the discussion of therepeater 582 and its operation are not shown in FIG. 12. Repeater 582receives analogue signals from a line card 532 that services a customer524 via the line card's twisted pair 542.

In some embodiments of the present invention repeater 582 comprises acontroller 600, a V.90A modem 602 and a V.90D modem 604. Functionsperformed by controller 600 may be executed by hardware or software or acombination of hardware and software comprised in the controller oraccessed by the controller. Controller 600 is connected via control anddata lines 601 to V.90A modem 602 and V.90D modem 604. V.90A modem 602comprises an analogue front end (AFE) 606 and modem processing circuitry608. AFE 606 is connected to twisted pair 542. V.90D modem 604 isconnected to multiplexer 562 and therethrough via high-speed modem 560and twisted pair 538 to remote terminal 536 and to customer 524. It isassumed that customer 524 is connected to V.90 pair-gain system 580 by aV.90A modem 609.

In some embodiments of the present invention, controller 600 of repeater582 is designed to determine whether a call routed to or from a customer524 by central office 522 is a voice call (including herein any fax ornon-high speed modem call), or a fast modem call.

If a repeater 582 determines that a call between central office 522 anda customer 524 serviced by the repeater is a voice call, the repeaterperforms similarly to a conventional analog front end (AFE) of pair-gainsystems known in the art. Optionally, the signals passing from line card532 through repeater 582 are passed only through AFE 606 directly tomultiplexer 562. In some embodiments of the invention, in instances forwhich the call is a voice call, repeater 584 codes and decodes signalsusing a compounding algorithm, 8 bit resolution and a sampling rate of8000 samples per second.

Alternatively, repeater 582 is placed in parallel to a conventional AFE.In cases for which controller 600 determines that a voice call is beingestablished with customer 524, the controller “disengages” repeater 582and routes signals from and to the customer's line card 532 via theconventional AFE.

If, however, repeater 582 determines that the call is a fast modem call,repeater 582 digitizes downstream signals from central office 522 togenerate a DS0 data stream of PCM octets, which are not degraded by thepair gain system.

When repeater 582 is operating in V.90 call mode, analog data signalsreceived by V.90A modem 602 for customer 524 from central office 522 aredigitized by AFE 606 and demodulated into a bit stream by modemcircuitry 608 which is transmitted to V.90D modem 604. V.90D modem 604processes the bits it receives and converts them into PCM octetsaccording to the V.90 protocol and transmits the octets in a DS0 datastream to multiplexer 562. Multiplexer 562 multiplexes the DS0 streamwith DS0 data streams from other repeaters and/or conventional analoguefront ends and transmits the multiplexed data streams to remote terminal536.

In some embodiments of the present invention, data bits transmitteddownstream to V.90D modem 604 are buffered by a “downstream” buffer 610.V.90A modem 602 “writes” data bits that it generates on downstreamcyclic buffer 610 and V.90D modem 604 “reads” the bits from the buffer.Buffer 610 cushions temporary differences between a rate at which V.90Amodem 602 transmits data bits to modem V.90D and a rate at which V.90Dmodem is able to receive the data bits. Optionally buffer 610 is acyclic buffer.

PCM upstream data from V.90A modem 609 of customer 524 to central office522, which V.90D modem 604 receives via multiplexer 562, is processedinto a bit stream by V.90D modem 604 and transmitted to V.90A modem 602.V.90A modem 602 parses the bits that it receives into PCM octetsaccording to the V.90 protocol and transmits the octets as a V.90 PCMdata stream to line card 532. In some embodiments of the presentinvention, data bits transmitted upstream by V.90D modem 604 to V.90Amodem 602 are buffered by an “upstream” buffer 612. Optionally, buffer612 comprises a cyclic buffer.

In some embodiments of the present invention, AFE 606 has a resolutiongreater than or equal to 15 bits and converts analogue signals that itreceives from line card 532 to digital signals at a sampling rate equalto or greater than 8,000 samples per second. In some embodiments of thepresent invention, the sampling rate is greater than or equal to 9,600samples per second. In some embodiments of the present invention, thesampling rate is greater than or equal to 16,000 samples per second. Inembodiments of the present invention for which AFE 606 operates at asampling rate of 8000 samples per second, in order for AFE 606 togenerate an accurate digital data stream from analog input signals,sampling times at which signals from line card 532 are sampled aresynchronized, using methods known in the art, with times at which thesignals are transmitted.

As a result of the enhanced resolution and sampling quantization errorof the digital output signals from AFE 606 is substantially smaller thanthe quantization error in output signals of conventional analogue frontends. Therefore, when central office 522 receives V.90 data addressed tocustomer 524 a DS0 data stream generated by V.90D modem 604 responsivethereto reproduces the V.90 data accurately and the data can betransmitted to V.90A modem 609 of customer 524 at transmission rates upto 56 Kbps. As a result of the operation of repeater 582 in V.90 callmode, in accordance with an embodiment of the present invention,pair-gain system 580 supports transmission of V.90 data to customer 524at transmission rates up to 56 Kbps.

In some embodiments of the invention, modems 604 and 602 are connected,respectively, to a customer modem 609 and a server modem 553 forming acomposite modem connection. The composite connection includes a customerloop between customer modem 609 and modem 604 and a server loop betweenserver modem 553 and modem 602. In some embodiments of the invention,modems 602 and 604 perform similarly to gateways 36A and 36B accordingto any of the above described embodiments. For example, modems 602 and604 may perform only data pump (DP) tasks, DP tasks and some or all ofthe EC tasks or DP tasks and ECDC tasks. The establishment of theconnection, between modems 602 and modem 553 and between modems 604 and609 may be performed independent of each other or may be correlatedusing any of the methods described above for gateways 36A and 36B. It isnoted, however, that the time required to pass information betweenmodems 602 and 604 is generally much shorter than required tocommunicate between gateways 36A and 36B. Thus, for example, controller600 may more readily provide for concurrent entrance to a datatransmission stage on the connections between modems 604 and 609 andbetween modems 553 and 602.

In some embodiments of the invention, controller 600 determines whethera current call is a voice call or a fast modem call using any of themethods described above, such as the method described with reference toFIG. 10.

FIGS. 13A-C are a flowchart of the acts performed by controller 600 inestablishing a connection, in accordance with an embodiment of thepresent invention. FIGS. 13A-C shows only acts required to understandthe operation of repeater 582. Acts that relate to determining upstreamtransmission rates, which are shown occurring before determination ofdownstream rates are, in practice, generally temporally interleaved withacts executed in determining downstream data transmission rates. Theacts are shown sequentially for convenience of presentation.

At the establishment of a connection, repeater 582 operates in a voicecall mode (722). Upon detection of an off-hook state (724), repeater 582eavesdrops (726) on communication between central office 522 andcustomer 524. If (728) signals of a modem protocol handshake (e.g., theV.8 protocol) are determined, the handshake signals are analyzed (730),otherwise repeater 582 remains in voice mode (722). If (732) thehandshake signals represent agreement on a V.90 protocol, repeater 582waits (734) until the end of the modem protocol handshake is reached andswitches to a V.90 state, optionally within the 70 msec period betweenphase 1 and phase 2 of modem data pump negotiations (handshake).

Controller 600 controls (740) repeater V.90D modem 604 to set a maximumsupported downstream transmission rate, “RD_(C-MAX)” on the customerloop equal to 56 Kbps, which is the maximum rate of the V.90 protocol.At 742, modems on both communication loops then start Phase II of theV.90 handshake.

At 744, the modems of both of the loops perform Phase III of the V.90handshake in which the digital modems announce transmission rates thatthey can support. At 746 modems in both loops enter Phase IV of thehandshake. In Phase IV controller 600 pauses the handshake procedure,using for example any of the stalling and/or spoofing methods describedabove, until a “CP” sequence (defined in ITU-T V.90 9/98) is receivedfrom customer V.90A modem 609 and an “MP” sequence (ITU-T V.90 9/98) isreceived from server V.90D modem 553). The CP sequence defines adownstream data rate “RD_(C)” for the customer loop and comprises atransmit data signaling rate capability mask for the customer V.90Amodem 609. The MP sequence defines a maximum data receive rate forserver V.90D modem 553 and comprises a receive data signaling ratecapability mask for server V90.D modem 553.

At 748, controller 600 attempts to equalize the upstream rates on bothcommunication loops. To accomplish this, in some embodiments of thepresent invention, controller 600 determines a possible maximum upstreamrate for the customer loop from the transmission mask received in the CPsequence from customer V.90A modem 609 and receive rates supported byrepeater V.90D modem 604. Controller 600 compares the possible maximumcustomer loop upstream rate to the maximum server upstream rate receivedin the MP sequence from server V.90D modem 553. Controller 600 thencontrols repeater V.90D modem to set a maximum upstream rate for thecustomer loop equal to the minimum of the compared upstream rates.

Following setting of the maximum upstream rate on the customer loop,controller 600 sets the receive mask of repeater V.90D modem 604 equalto the receive mask of server V.90D modem 553. Repeater 600 also setsthe transmission mask of repeater V.90A modem 602 equal to thetransmission mask of customer V.90A modem 609. However, if thetransmission mask supports upstream rates greater than the maximumcustomer loop upstream rate, the controller adjusts the transmissionmask of repeater V.90A modem 602 so that the maximum upstream rate ofthe transmission mask is equal to the maximum upstream rate of thecustomer loop.

It is to be noted that controller 600 will, in general, be able tocontrol the rate negotiations by controlling repeater modems 602 and 604so that the upstream rates on the customer and server loops are thesame. Equalization of the upstream rates is only impossible if a bitrate on one of the loops is equal or less than 2,600 bps and a symbolrate on the other loop is greater than or equal to 2,743 symbols persecond.

In a decision 750, if controller 600 determines it cannot establish asame upstream data transmission rate for both loops, repeater 582abandons attempts to set up a V.90 call between customer 524 and modem553 and controller 600 terminates the V.90 handshake and switchesrepeater 582 to voice mode (722). If on the other hand controller 600 issuccessful in establishing equal upstream rates for both loops,controller 600 compares (754) downstream rate RD_(C) negotiated on thecustomer loop by V.90A customer modem 609 and V.90D repeater modem 604to a downstream rate RD_(S) on the server loop negotiated by repeaterV90A modem 602 and server V90D modem 553. If (756) RD_(C)>RD_(S),controller 600 controls (758) repeater modem V.90D to setRD_(C-MAX)=RD_(S). Thereafter, a cycle counter “N” is incremented (760)by 1 and if (762) N≧N_(M), repeater 582 reverts to voice mode (722). If,on the other hand, N<N_(M), controller 600 attempts another attempt toachieve equal rates on both loops by returning to Phase II (742) with anewly determined RD_(C-MAX).

If (756) RD_(C)≦RD_(S), RD_(S) is set (764) equal to RD_(C) and repeatermodem 602 chooses a “downstream” constellation that supports thedownstream rate RD_(C). At 766, both communication loops complete PhaseIV of the handshake, i.e., modem 602 transmits a CP sequence to servermodem 553 and repeater modem 604 transmits an MP sequence to customermodem 609.

At 770, controller 600 initializes upstream and downstream buffers 610and 612 and synchronizes repeater modems 602 and 604 so that theyinitiate data transmission at a substantially same time. Datatransmission between customer V.90A modem 609 and server modem 553 takesplace thereafter in accordance with the V.90 protocol in a step 772.

In some embodiments of the invention, initializing cyclic buffers 610and 612 comprises writing a block of binary ones in each buffer so as toseparate the read pointer from the write pointer. The block of binaryones will not generate transmission errors at onset of data transmissionsince binary ones at the beginning of data transmission is consideredpart of training by the V.90 protocol. Thereafter, inequalities intransmission rates between the customer loop and the server loop may begenerated that cause the read pointer to reach the write pointer, or thewrite pointer to reach the read pointer from behind on a buffer 610 or612. When this occurs on a buffer, controller 600 writes a block ofbinary ones to the buffer. The block of ones generates a transmissionerror that causes the ECDC protocol deployed by modems 609 and 553 toinitiate retransmission of data in the buffer. Optionally, the buffersize is such that it can contain more than one modem frame of data andless than two modem frames of data. As a result, a temporary mismatch intransmission rates that results in a block of ones being written to abuffer during data transmission will cause retransmission of at most twodata frames.

If (774) during data transmission an event occurs that triggers raterenegotiation on one of the loops, controller 600 controls (776)repeater modems 602 and 604 so that rate renegotiation begins on bothloops and the controller returns to step 744. Similarly, if (778) duringdata transmission an event occurs that triggers retraining on one of theloops, controller 600 controls (780) the repeater modems so thatretraining begins on both loops and the controller returns to step 742.

It should be noted that whereas repeater 582 has been described foradapting a communication channel for data transmission according to theV.90 protocol, repeaters similar in construction and concept can beconstructed to adapt communication channels for transmission of dataaccording to other fast modem protocols.

Furthermore, pairs of modems, similar to modems 602 and 604 may be usedto prevent signal degradation on communication channels other thanpair-gain channels in which a plurality of digital to analog conversionsare performed.

It is noted that although the above description relates to connectionswhich include two modem connection segments and a packet based segment,some embodiments of the invention pertain to connections which have moreor fewer modem connection segments. For example, a connection may beformed of three modem connection segments connected through twopacket-based segments. Such a connection may be formed, for example,when a call passes between a plurality of telephone and/or IP suppliers.

FIG. 14 is a schematic illustration of a distributed remote accessserver (RAS) system 800, in accordance with an embodiment of the presentinvention. System 800 comprises a plurality of front end units 802located close to client modems 804, e.g., within the distance of a localarea telephone call. Client modems 804 service, for example, computers812 and/or other processors which connect through client modems 804 to agateway 810 of RAS system 800. The connections between client modems 804and front end units 802 generally pass over analog and/or digitaltelephone switched lines 814. A central upper layer unit 806 isconnected to front end units 802 over communication links 808. Upperlayer unit 806 is connected to gateway 810 which optionally leads to apublic packet based network, e.g., the Internet.

Optionally, communication links 808 comprise packet based networks,e.g., IP, frame relay or ATM networks. Alternatively or additionally,one or more of communication links 808 comprises any other type of link,which is not a VBM link, for example a high bandwidth synchronous link.Communication links 808 may optionally be over physical wires, wirelesslinks or a combination thereof. In some embodiments of the invention,one or more of communication links 808 comprises a multi-point networkwhich connects a plurality of different units and/or an addressablenetwork in which signals may be transmitted from a source to a pluralityof destinations. Alternatively or additionally, one or more ofcommunication links 808 comprises a dedicated link for connectingbetween front end unit 802 and upper layer unit 806. Communication links808 may be of substantially any length including long lengths of tens,hundreds thousands or tens of thousands of kilometers.

In some embodiments of the invention, client modem 804 comprises astandard modem which is not altered in order to perform the presentinvention. Furthermore, in some embodiments, client modem 804 does notknow whether it is connected to a distributed RAS or to a regular, priorart, RAS.

As is known in the art, the signals transmitted between client modems804 and front end units 802 may represent data bits to, or from,computer 812, or may comprise control signals of one of the layers ofthe VBM connection, i.e., data pump (DP), error correction (EC) or datacompression (DC).

In some embodiments of the invention, front end unit 802 performs datapump (DP) tasks and upper layer unit 806 performs error correction (EC)and data compression (DC) tasks. Signals transmitted from client modem804 which represent data bits are demodulated by front end unit 802 intodata bits. The demodulated data bits are optionally encapsulated intopackets and/or into any other format required by the communication link808 connecting the front end unit 802 to upper layer unit 806. Theencapsulated packets are optionally transmitted on a packet connection(e.g., UDP or TCP) on communication link 808 to upper layer unit 806.Upper layer unit 806 removes the encapsulation from the packets itreceives and performs EC and DC tasks on the bits extracted from thepackets.

Data bits transmitted to computer 812 are received by upper layer unit806 through gateway 810. The received data bits are compressed by upperlayer unit 806 in accordance with the DC layer tasks and errorcorrection (EC) bits are annexed to the bits in accordance with the EClayer tasks. The compressed bits, along with the annexed EC bits, arethen encapsulated into packets and transmitted over communication link808 to front end unit 802. Front end unit 802 removes the encapsulation,modulates the bits and transmits the modulated data signals to clientmodem 804.

In some embodiments of the invention, front end unit 802 examines thecontents of the signals passed to upper layer unit 806 to determinewhether the signals include information. Alternatively or additionally,upper layer unit 806 examines the contents of the signals passed tofront end unit 802. Signals which do not include information, i.e.,signals which include padding sequences defined by modemrecommendations, such as long sequences of ‘1’ bits or idle ECDC 7Esignals, are optionally discarded. Optionally, all padding flags arediscarded. Alternatively, only padding sequences beyond a predeterminedlength, are discarded.

In some embodiments of the invention, the discarded padding flags arereplaced by control packets, transmitted, for example, on a separateconnection, which state the number and/or nature of the discarded bitsso that the discarded signals are easily filled in by the receivingunit. Alternatively, control signals are not transmitted instead of thediscarded signals and the missing signals are filled in based on thetransmission rate on the VBM connection. By discarding signals which donot carry information, the load on link 808 is reduced allowing higherutilization rates of the link.

Front end unit 802 and client modem 804 exchange DP control signals asrequired by the standard governing the VBM connection. DP controlsignals transmitted to client modem 804 are generated by front end unit802 and DP control signals from client modem 804 are handled by frontend unit 802. In some embodiments of the invention, the DP controlsignals are generated by front end unit 802, independently, withoutreceiving instructions and/or information from upper layer unit 806.Alternatively, upper layer unit 806 instructs front end unit 802 on theDP control signals it should transmit and/or provides front end unit 802with information used in generating the DP signals.

In an exemplary embodiment of the invention, during a stage used todetermine the round trip delay of the connection, e.g., the second stageof the V.34 negotiation, front end unit 802 does not respond at theprescribed time (e.g., after the prescribed 40 msec) to the signals itreceives. Instead, front end unit 802 waits an additional time whichrepresents the round trip delay period of signals on link 808 betweenfront end unit 802 and upper layer unit 806 which calculates time-outs.Optionally, the additional wait time is a predetermined estimate of thedelay of link 808. Alternatively, front end unit transmits a timemeasuring signal to upper layer unit 806 and the time between thetransmission and receiving the response is used as the additional waittime. The time measuring signal may be transmitted before or after thesignal to which front end unit 802 must respond, is received.Alternatively or additionally, the changes during the stage ofdetermining the round trip delay are performed as described in Israelpatent application 140,952, filed Jan. 17, 2001, the disclosure of whichis incorporated herein by reference.

Optionally, EC and DC control signals are forwarded by front end unit802 as if they are data bits, without front end unit 802 differentiatingbetween data bits and the bits of EC and DC control signals.Alternatively, front end unit 802 recognizes EC and DC control signalsreceived from client modem 804 and transmits their bits to upper layerunit 806 separately from the data bits, on the same connection used fordata bits or on a different connection. Similarly, front end unit 802optionally receives EC and DC control signals from upper layer unit 806(for transmission to client modem 804), separately from data bits.

In some embodiments of the invention, the packet connections on link 808are in accordance with a delivery confirming protocol (e.g., TCP or aproprietary protocol above UDP), so that signals are generally not loston their way between front end unit 802 and upper layer unit 806.Alternatively, the packet connections on link 808 are in accordance witha non-confining protocol (e.g., UDP) which generally incurs less delayon the transmitted signals. Generally, mistakes which occur in thetransmission will be corrected by the EC tasks performed by upper layerunit 806 and client modem 804. Further alternatively or additionally, aredundancy method, for example double transmission, is used for theexchange of data bits on link 808. Optionally, different redundancymethods are used for data bits and for control bits according to theirimportance. Alternatively, redundancy is used only for control signalsor only for data bits. In some embodiments of the invention, additionalprotocols are applied to the signals transmitted on link 808. Forexample, the signals transmitted on link 808 may be encrypted, e.g., inaccordance with the IPsec protocol, before they are transmitted, inorder to prevent eavesdropping to the VBM connection.

Optionally, the RAS control signals exchanged between front end unit 802and upper layer unit 806 are transmitted on the same packet connectionas the data bits and/or EC and/or DC control signals. Alternatively oradditionally, a separate control connection on communication link 808 oron a separate link is used to exchange RAS control signals and/or ECand/or DC control signals between front end unit 802 and upper layerunit 806. Substantially any agreed format may be used for the controlsignals exchanged between front end unit 802 and upper layer unit 806,for example a format similar to that described in the ITU T.38recommendation. The separate control connection may be a deliveryconfirming connection or a non-confirming connection, with or withoutredundancy.

In some embodiments of the invention, front end unit 802 performs datapump (DP) and error correction (EC) tasks while upper layer unit 806performs data compression (DC) tasks.

Signals, transmitted from client modem 804, which represent data, aredemodulated by front end unit 802 into data bits. The demodulated databits are then checked for errors according to error correction bitsannexed thereto. If an error occurred, front end unit 802 requests aretransmission of the erroneous data from client modem 804. The errorfree data bits in their compressed form are encapsulated and forwardedto upper layer unit 806, using any of the encapsulation methodsdescribed above. In addition, any of the types of connections describedabove may be used for transmission of the data bits on link 808. It isnoted, however, that the consequences of transmission errors on link 808which are not handled by the connection on link 808, are less severewhen the EC tasks are performed by upper layer unit 806. This is becausethe transmission errors on link 808 will be identified and handled bythe EC tasks of the modem. Conversely, when the EC tasks are performedby front end unit 802, uncompensated errors on link 808 will only beidentified, if at all, by an application or transport layer above themodem.

Data bits transmitted to computer 812 are received by upper layer unit806 through gateway 810. The received data bits are compressed by upperlayer unit 806 and are then encapsulated and transmitted to front endunit 802. Front end unit 802 removes the encapsulation, annexes errorcorrection (EC) bits to the data bits in accordance with the EC layertasks, modulates the bits and transmits the modulated data signals toclient modem 804.

Front end unit 802 and client modem 804 exchange DP control signals asdescribed above. In addition, EC control signals are generated andhandled by front end unit 802. On the other hand, DC control signals areforwarded by front end unit 802, with or without being aware of theirbeing DC control signals.

In some embodiments of the invention, front end unit 802 and upper layerunit 806 handle their control signals independently, without receivinginformation and/or instructions from the other unit. Alternatively oradditionally, one or more of units 802 and 806 receives informationand/or instructions from the other unit and accordingly generates atleast one of its control signals.

In some embodiments of the invention, front end unit 802 performs datapump (DP) and HDLC tasks while upper layer unit 806 performs LAPM anddata compression (DC) tasks.

Signals transmitted from client modem 804 which represent data aredemodulated by front end unit 802 into data bits. Padding flags and theCRC field are removed from the demodulated data bits, and erroneousframes are discarded. The resulting frames are encapsulated andforwarded to upper layer unit 806, using any of the encapsulationmethods described above. Upper layer unit 806 acknowledges the receiptof the frames and exchanges flow control commands (e.g., retransmissionrequests, buffer full notices) with client modem 804. Upper layer unit806 also decompresses the data bits extracted from the frames.

Data bits transmitted to computer 812 are received by upper layer unit806 through gateway 810. The received data bits are compressed by upperlayer unit 806 and are broken into frames to which flow control commandsare annexed. The frames are encapsulated and transmitted to front endunit 802. Front end unit 802 removes the encapsulation, performs flagpadding and adds a CRC field to the frames in accordance with the HDLClayer tasks. Front end unit 802 then modulates the bits and transmitsthe modulated data signals to client modem 804.

Front end unit 802 and client modem 804 exchange DP control signals asdescribed above. Optionally, delay procedures as described above areused during the stage in which the round trip delay is measured. Inaddition, HDLC control signals are generated and handled by front endunit 802. On the other hand, LAPM and DC control signals are forwardedby front end unit 802, with or without being aware of their being DCcontrol signals.

In some embodiments of the invention, front end unit 802 and upper layerunit 806 do not exchange any RAS control signals (i.e., signals used tocoordinate the operations of the RAS between front end unit 802 andupper layer unit 806) except for signals for establishment and closingof packet connections. Alternatively, front end unit 802 and upper layerunit 806 exchange RAS control signals, for example to provideinformation and/or instructions from upper layer unit 806 to front endunit 802 regarding the generation of DP signals. Alternatively oradditionally, the RAS control signals are used by front end unit 802 toindicate to upper layer unit 806 entering and/or exiting a datatransmission mode and/or the transmission rate of signals in the DPlayer. Further alternatively or additionally, the RAS control signalsare used to notify front end unit in disconnect events and/or for flowcontrol purposes between the units.

In some embodiments of the invention, a division of the tasks of RASsystem 800 between front end unit 802 and upper layer unit 806 isperformed dynamically. Optionally, upper layer unit 806 may operate witha plurality of front end units 802 which perform different tasks. Atformation of a connection with a front end unit 802, upper layer unit806 determines the tasks performed by the front end unit 802 andaccordingly adjusts the tasks it is to perform. Alternatively oradditionally, a front end unit 802 may operate with a plurality ofdifferent upper layer units 806 which perform different tasks. The tasksperformed by front end unit 802 are adjusted according to the tasksperformed by the upper layer unit 806.

Alternatively or additionally, the task division between front end unit802 and upper layer unit 806 is chosen responsive to the load on frontend unit 802 and/or on upper layer unit 806. In some embodiments of theinvention, at formation of a connection between front end unit 802 andupper layer unit 806, the units exchange indications of their load andaccordingly choose the task division to be used on the connection.

In an exemplary embodiment of the invention, front end unit 802generally performs tasks having a maximal load, leaving upper layer unit806 with a minimal processing load. Thus, upper layer unit 806, whichservices a larger number of potential users, is left with as much aspossible free processing power. When front end unit 802 is close to itsmaximal power consumption, the front end unit 802 performs, optionallyonly on newly accepted connections, only a minimal set of tasks (e.g.,only DP tasks).

In some embodiments of the invention, front end unit 802 manages a setof thresholds to which the processing load of front end unit 802 iscompared. For example, if the load of front end unit 802 is above 50% ofits processing power, front end unit 802 performs on a newly acceptedconnection only part of the EC tasks. If the load of front end unit 802is above 75% of its processing power, front end unit 802 performs on thenew connection only DP tasks. In some embodiments of the invention, atsome load rates and/or for some connections, front end unit 802 mayperform all the modem tasks for a connection, including the DC tasks.

It is noted that front end unit 802 and/or upper layer unit 806 mayallow overbooking of connections beyond their processing power based onstatistical measures. The scheduling in overbooked connections may beperformed, for example, as described in U.S. patent application Ser. No.08/969,981 filed Nov. 13, 1997, PCT application PCT/IL00/00733 filedNov. 9, 2000 or in PCT application PCT/IL01/00132 filed Feb. 8, 2001,the disclosures of which are incorporated herein by reference.Specifically, by performing all the DC tasks in upper layer unit 806,rather than in a plurality of front end units 852, the overbooking ratewhich can be used is greater, as the variance decreases with theincrease in the number of connections handled.

Alternatively or additionally to determining the task divisionresponsive to the load on front end unit 802, the task division isdetermined responsive to the load on upper layer unit 806. Thedetermination of the task division may be performed by a single unit(i.e., front end unit 802, upper layer unit 806, or a different unit)which then transmits instructions to the other unit(s) on the tasks theyare to perform. Alternatively, the information on the load of the frontend unit 802 and/or upper layer unit 806 is distributed between theunits which determine the task distribution according to a predeterminedprotocol.

Alternatively or additionally to determining the task distributionresponsive to the load on front end unit 802 and/or upper layer unit806, the task distribution is determined responsive to the line qualityof the connection on link 808, e.g., the jitter and/or delay of thelink. For example, when the line quality of link 808 is high, preferenceis given to front end unit 802 performing EC tasks, while when thequality of link 808 is low preference is given to upper layer unit 806performing the EC tasks. In some embodiments of the invention, theselection of whether to use a delivery confirming protocol is performedresponsive to the quality of link 808.

Further alternatively or additionally, the distribution of the tasks isdetermined responsive to the quality of service (QoS) of the newconnection. For example, high QoS connections may have the EC tasksperformed at front end unit 802, closer to client modem 804, to allowfaster retransmission of erroneous signals.

Further alternatively or additionally, the distribution of the tasks isperformed responsive to user settings and/or responsive to one or moreexternal attributes, such as the time of day, date, weather, etc. Forexample, statistics may be gathered on the use of client modems 804 indifferent areas at different times or seasons. Front end units 802 willoptionally be set to perform minimal tasks at times in which peak usageis expected in their area. Possibly, when peak usage is expectedthroughout a region of an upper later unit 806, the distribution isplanned to achieve a maximal total number of connections.

In some embodiments of the invention, when a client modem 804 requestsestablishment of a modem connection while front end unit 802 is entirelyloaded, front end unit 802 negotiates with upper layer unit 806 thetransfer of some of the tasks (e.g., EC tasks) of one or more of thehandled connections to upper layer unit 806, to allow the connection ofthe new client modem.

In an exemplary embodiment of the invention, in the transfer of one ormore tasks between the units, the EC flow control is used to stop thetransmission of data on the connection for a short period. The handlingof the data currently accumulated is completed and the handling of theone more tasks is transferred between front end unit 802 and upper layerunit 806. The EC flow control then resumes the data transmission.Alternatively or additionally, the transfer of one or more tasks isperformed without stopping the transmission of data. Optionally, intransferring the handling of a task, a state record of the task istransmitted from the unit stopping to handle the task to the unit takingover the handling of the task.

Allowing dynamic distribution of the tasks between upper layer unit 806and front end unit 802 allows achieving a higher utilization of theapparatus of system 800. On the other hand, using a fixed distributionof tasks may allow use of cheaper hardware and/or software for theapparatus of system 800.

FIG. 15 is a schematic block diagram of a public switching telephonenetwork (PSTN) 850 with off-loading capabilities, in accordance with anembodiment of the present invention. PSTN 850 comprises a plurality offrond end units 852 which are located close to client modems 804, e.g.,adjacent digital loop carriers (DLCs) 860 and/or central offices (COs)854. When a client modem 804 requests to establish a call with a modemRAS 858, for example of an ISP which supports off-loading, the call isidentified by PSTN 850, e.g., by an adjacent CO 854 or DLC 860, and thecall is routed through an adjacent front end unit 852. From front endunit 852, the call is directed over an off loading network 862 to anupper layer unit 856 of RAS 858 to which the call is directed. The RAS858 to which the call is directed is optionally determined according tothe dialed telephone number. Alternatively or additionally, any otheroff-loading method is used to determine which RAS 858 is to handle theconnection. In some embodiments of the invention, the VBM connectionshandled by a single front end unit 852 may receive upper layer handlingfrom a plurality of different upper layer units 856. Similarly, a singleupper layer unit 856 may handle VBM connections which received front endhandling from a plurality of different front end units 852.

Optionally, off-loading network 862 comprises a non-switched network,for example, a packet based network. Alternatively or additionally,off-loading network 862 comprises any other data link, for example ahigh bandwidth synchronous link.

The VBM tasks, which are to be performed in handling the connection withclient modem 804, are divided between front end unit 852 and upper layerunit 856 in accordance with any of the static or dynamic divisionsdescribed above with reference to FIG. 1.

It is noted that, in these divisions, upper layer unit 856 of RAS 858performs the entire PPP handling and front end unit 852 does not need tohandle tasks of the PPP protocol. This simplifies the apparatus of frontend unit 852. Furthermore, as the DC tasks are performed by upper layerunit 856, the signals passing on the link between front end unit 852 andupper layer unit 856 are already compressed and additional compressionis not required. Thus, there is no need for front end unit 852 toperform an additional compression (e.g., L2TP compression) which isgenerally computation intensive.

In some embodiments of the invention, front end unit 852 is used, inaddition to its use in off-loading, for modem over IP connections asdescribed above with reference to gateways 36. Optionally, when a CO 854of network 850 identifies that a call is directed to a remote modem ormodem RAS, for example, which does not support off-loading, the call isoff-loaded through a pair of front end units 852, so as to form a modemover IP (MoIP) connection. Alternatively or additionally, the MoIPconnection is routed through two front end units 852 which are notconnected through a switched network or at a time at which no switchedlines are available.

The two front end units 852 along the path of the MoIP connectionperform the same modem tasks. Optionally, when front end units 852support dynamic division of tasks, at the establishment of a connectionand/or when a retrain occurs, front end units 852 negotiate between themwhich tasks they are to perform, for example as described above withreference to gateways 36A and 36B. Alternatively, as described above,tasks may be transferred between front end unit 852 and upper layer unit856 during data transfer on the connection. In some embodiments of theinvention, when front end units 852 participate in a MoIP connectionthey correlate between them the DP, EC and/or DC control signals whichthey transmit to their respective end modems. The control signalcorrelation may be performed as described above and/or in Israel patentapplications 136,775, filed Jun. 14, 2000, 140,734, filed Jan. 4, 2001,or 140,952, filed Jan. 17, 2001, 142,379, filed Apr. 2, 2001 or in PCTapplication IL00/00492 filed Aug. 13, 2000, the disclosures of which areincorporated herein by reference. Other correlation procedures may bederived by altering fast fax correlation procedures, such as theprocedures for the V.34 half duplex protocol described in PCTapplication PCT/IL00/00657, filed Oct. 17, 2000, the disclosure of whichis incorporated herein by reference.

Optionally, when a connection is established through front end unit 852,front end unit 852 is notified the type of the connection (e.g.,off-loading, MOIP) so that it determines whether control signalcorrelation is required for the connection and/or which type ofcorrelation is required. Alternatively or additionally, front end unit852 begins performing signal correlation for each established connectionuntil or unless it is instructed otherwise by upper layer unit 856.

By using the same front end units 852 for both off-loading and MoIPconnections, the costs of infrastructure required by networkimplementers are reduced.

FIG. 16 is a flowchart of the acts performed by a CO 854 in accepting aconnection, in accordance with an embodiment of the present invention.Upon receiving (900) a new connection, CO 854 determines (902) whetherthe connection is a modem connection. If the connection is a modemconnection, CO 854 determines (904) whether the connection is directedto a RAS which supports off-loading, using any method known in the art,for example based on the phone number dialed. If the connection isdirected to a RAS which supports off-loading, the connection is passed(908) through front end unit 852. If the connection is not directed to aRAS which supports off-loading, CO 854 determines (906) whether theconnection is directed to a remote location which warrants the use of aMoIP connectional. For example, local calls may be considered notrequiring MoIP off-loading, while long distance calls may be consideredas requiring MoIP off-loading.

If the connection requires MoIP off-loading, CO 854 determines (910)whether a remote front end unit 852, adjacent to the recipient of themodem connection, is compatible with the front end unit 852 adjacent CO854. If (910) the front end units are compatible, the connection ispassed (912) through the adjacent front end unit 852 and the remotefront end unit 852 to perform a MoIP connection.

Referring in more detail to determining (902) whether the connection isa modem connection, in some embodiments of the invention, in forming theconnection, client modem 804 transmits a modem identification signal,e.g., a 2100 Hz signal, which notifies a modem on the other end that theconnection is a modem connection. CO 854 identifies the modemidentification signal and accordingly determines that the connection isa modem connection. Alternatively or additionally, the determination isbased on the telephone number dialed which is included in a list ofmodem numbers.

In some embodiments of the invention, the connection is establishedusing connection establishment procedures substantially as used forestablishing voice over IP (VoIP) connections, for example, theprocedures of the H.323 protocol and/or the session initiation protocol(SIP). In forming the connection, one or more packet connections areoptionally established for communication between front end unit 852 andupper layer unit 856.

In some embodiments of the invention, front end units 852 handle allconnections in substantially the same manner regardless of whether theyare handling a MoIP connection or an off-loaded connection.Alternatively, the handling of at least some of the MoIP connectionsdiffers from the handling of off-loaded connections in the manner inwhich they generate control signals. For example, MoIP connections maycorrelate the rates of operation of the DP tasks of the connections fromthe front end units 852 to the end modems, while in off-loadingconnections such correlation is not performed.

It is noted that although the above description relates to distributionof the tasks of a RAS between two units, in some embodiments of theinvention the tasks of the RAS are distributed between three or moreunits. For example, a front end unit performs DP tasks, a regional unitperforms EC tasks and a central unit performs DC tasks.

Although the above description relates to communication with a clientmodem 804 which performs DC, EC and DP tasks, the present invention maybe performed also with client modems which perform other sets of modemtasks, for example modems which perform only the EC and DP tasks. Forexample, a connection with a client modem 804 which performs only EC andDP tasks may be terminated by a front end unit which handles DP tasksand an upper layer unit which performs EC tasks.

It is noted that although some of the above exemplary embodiments relateto specific example protocols, such as the V.34 full duplex protocol,the present invention is not limited to any specific protocol and may beimplemented with relation to substantially any other modem protocol(e.g., V.22, V.32, V.32bis, V.90, V.91, V.92). In addition, some of theprinciples of the present invention may be used with relation to othertypes of point to point modem connections (passing on segments which maybe multi-point) and are not limited to VBM modem connections.

For example, in some embodiments of the invention, stalling or spoofingsignals are used in order to stall the progression of the negotiationson one modem connection while waiting for information from anotherconnection. For each specific protocol, a method in accordance with theprotocol is used to stall the negotiation of a connection untilinformation on the parameters of a peer connection are received. In someembodiments of the invention, the stalling includes transmitting signalsbeyond their usual transmission time, and/or transmitting guess valuesand initiating a retrain or a re-negotiation if the guess signals hadincorrect values. Alternatively or additionally, the stalling includestransmitting corrupted signals which are recognized by the other endmodem as belonging to the protocol but do not fit into the specificrequirements from the signal which allow proceeding of the negotiation.

It is noted that in some of the modem protocols the required timingconstraints are so tight during the negotiation procedure, such that inmany cases the negotiation procedure for achieving equal upstream and/ordownstream transmission rates on the modem connections requires aretrain procedure. In some embodiments of the invention, during aprotocol negotiation procedure, e.g., the V.8 procedure, gateways 36Aand/or 36B prevent the selection of these protocols to avoid the extraconnection time required for the retrain. Alternatively, the user ofcall modem 32A may select whether or not to forego protocols thatrequire a retrain. Further alternatively, gateways 36A forego a protocolthat requires retrain only if another protocol having similarcharacteristics may be chosen.

Data and control signals transmitted between modems, gateways, and othercommunication units may appear in various forms. Some of the signals aremodulated while others are demodulated. The bit content of some of thesignals may be, for example, in frames, cells or in streams. The signalsmay be transmitted along with various header and/or tail fields whichare specific to the medium on which the signals are transmitted.

It will be appreciated that the above-described methods may be varied inmany ways, including, changing the order of steps, and the exactimplementation used. It should also be appreciated that theabove-described description of methods and apparatus are to beinterpreted as including apparatus for carrying out the methods andmethods of using the apparatus.

The present invention has been described using non-limiting detaileddescriptions of embodiments thereof that are provided by way of exampleand are not intended to limit the scope of the invention. It should beunderstood that features and/or steps described with respect to oneembodiment may be used with other embodiments and that not allembodiments of the invention have all of the features and/or steps shownin a particular figure or described with respect to one of theembodiments. Variations of embodiments described will occur to personsof the art.

It is noted that some of the above described embodiments may describethe best mode contemplated by the inventors and therefore may includestructure, acts or details of structures and acts that may not beessential to the invention and which are described as examples.Structure and acts described herein are replaceable by equivalents whichperform the same function, even if the structure or acts are different,as known in the art. Therefore, the scope of the invention is limitedonly by the elements and limitations as used in the claims. When used inthe following claims, the terms “comprise”, “include”, “have” and theirconjugates mean “including but not limited to”.

1. A method of performing a negotiation session on a modem connection,comprising: receiving in a negotiation session a plurality ofnegotiation signals, including a plurality of data pump negotiationsignals and a plurality of signals having a bit content, from a sourcemodem, by a first gateway; forwarding the content of at least one of thereceived data pump negotiation signals from the first gateway to aremote unit; receiving, by the first gateway, responses to at least oneof the forwarded data pump negotiation signals from the remote unit;forwarding a response to at least one of the data pump negotiationsignals received from the source modem, by the first gateway to thesource modem, responsive to receiving a response from the remote unit;and transmitting from the first gateway to the source modem, responsesignals, that allow the proceeding of the negotiation session by thesource modem, to at least one of the received negotiation signals havinga bit content, regardless of whether a response to the at least one ofthe signals was sent or received from the remote unit.
 2. A methodaccording to claim 1, wherein forwarding a response by the first gatewayto the source modem, responsive to receiving responses from the remoteunit comprises forwarding at least some of the responses received fromthe remote unit without altering their information content.
 3. A methodaccording to claim 1, wherein forwarding a response by the first gatewayto the source modem, responsive to receiving responses from the remoteunit comprises forwarding at least some of the responses received fromthe remote unit with an altered information content.
 4. A methodaccording to claim 1, wherein transmitting response signals from thefirst gateway to the source modem comprises transmitting at least someof the response signals without forwarding the signals to which theresponse signals respond, to the remote unit.
 5. A method according toclaim 1, wherein, in response to at least some of the negotiationsignals from the source modem, the first gateway both transmits responsesignals to the source modem and forwards the contents of the negotiationsignals to the remote unit.
 6. A method according to claim 5, whereintransmitting response signals from the first gateway to the source modemcomprises transmitting at least some of the response signals afterforwarding the signals to which the response signals respond to theremote unit but before receiving a response thereto.
 7. A methodaccording to claim 5, wherein in response to at least some of thenegotiation signals from the source modem, the first gateway bothtransmits response signals to the source modem, which include guessvalues of one or more parameters and forwards response signals from theremote unit which include final values of the one or more parameters. 8.A method according to claim 7, comprising initiating a retrain by thefirst gateway between transmitting the response signals to the firstmodem and forwarding the response signals from the remote unit.
 9. Amethod according to claim 5, wherein the first gateway both transmitsresponse signals to the source modem and forwards the negotiationsignals to the remote unit substantially concurrently.
 10. A methodaccording to claim 1, wherein transmitting from the first gateway to thesource modem, response signals to at least one of the receivednegotiation signals comprises transmitting response signals to at leastone data pump (DP) negotiation signal.
 11. A method according to claim1, wherein transmitting from the first gateway to the source modem,response signals to at least one of the received negotiation signalscomprises transmitting response signals to at least one error correction(EC) negotiation signal.
 12. A method according to claim 1, wherein thesignals which the first gateway forwards to the remote unit comprisesignals for calculation of the round trip delay of the modem connection.13. A method according to claim 1, wherein forwarding the content of atleast one of the received data pump negotiation signals to the remoteunit comprises forwarding substantially the same bit content.
 14. Amethod according to claim 1, wherein forwarding the content of at leastone of the received data pump negotiation signals to the remote unitcomprises forwarding only a partial portion of at least one of thereceived signals.
 15. A method according to claim 1, wherein forwardingthe content of at least one of the received data pump negotiationsignals to the remote unit comprises forwarding over a network pathwhich has a round trip delay greater than the maximal time defined forresponding to at least one of the negotiation signals from the sourcemodem.
 16. A method according to claim 1, wherein the remote unitcomprises a second gateway.
 17. A method according to claim 1, whereinthe remote unit is connected to the first gateway through an addressablenetwork.
 18. A method according to claim 17, wherein the remote unit isconnected to the first gateway through a packet based network.
 19. Amethod according to claim 1, wherein receiving a plurality ofnegotiation signals from the source modem comprises receivingnegotiation signals of a plurality of negotiation stages.
 20. A methodaccording to claim 19, wherein the first gateway does not forwardresponse signals from the remote unit for signals of a first group ofone or more stages.
 21. A method according to claim 20, whereinsubstantially all the response signals to signals of at least one of thestages are generated by the first gateway without relation toinformation received from units other than the source modem.
 22. Amethod according to claim 19, wherein all the response signalstransmitted by the first gateway in response to signals of a secondgroup of one or more stages are based on responses received from theremote unit.
 23. A method according to claim 22, wherein the responsesignals transmitted by the first gateway in response to signals of thesecond group of one or more stages are transmitted as if they are datasignals.
 24. A method according to claim 22, wherein the second group ofstages comprises at least one ECDC negotiation stage.
 25. Acommunication gateway, comprising: a switched network interface adaptedto receive a plurality of negotiation signals, having a bit content,from a source modem; an addressable network interface adapted to forwardnegotiation signals to a remote gateway; and a controller adapted toforward through the addressable network interface at least some of, butnot all, the negotiation signals received through the switched networkinterface during a specific connection, including at least one data pumpnegotiation signal and which is adapted to generate a response, thatallows the proceeding of the negotiation session by the source modem,transmitted through the switched network interface to at least some of,but not all, the negotiation signals received through the switchednetwork interface during the specific connection.
 26. A gatewayaccording to claim 25, wherein the controller is adapted to forwardthrough the addressable network interface substantially the entire bitcontent of at least some of the negotiation signals received through theswitched network interface.
 27. A gateway according to claim 25, whereinthe controller is adapted to forward through the addressable networkinterface a portion including less than the entire bit content of atleast some of the negotiation signals received through the switchednetwork interface.
 28. A gateway according to claim 25, wherein theaddressable network interface comprises a packet based networkinterface.
 29. A method according to claim 1, wherein receiving theplurality of negotiation signals comprises receiving signals of a fullduplex negotiation session.
 30. A method according to claim 1, whereinreceiving the plurality of negotiation signals comprises receivingnegotiation signals of a non-facsimile modem session.
 31. A method ofperforming a negotiation session on a modem VBM connection, comprising:receiving a plurality of negotiation signals, having a bit content, froma source modem, by a first gateway; transmitting from the first gatewayto the source modem, one or more first response signals, in response toat least one of the received signals from the source modem; receiving,by the first gateway, at least one parameter of a remote modemconnection from a remote unit, after transmitting the one or more firstresponse signals; initiating a retrain by the first gateway aftertransmitting the one or more first response signals, but beforetransmitting data signals on the modem connection; and retransmittingfrom the first gateway to the source modem, the one or more firstresponse signals, after initiating the retrain, wherein theretransmitted first response signals include one or more parametervalues set according to the at least one parameter of the remote modemconnection.
 32. A method according to claim 31, wherein receiving atleast one parameter of a remote modem connection comprises receiving anindication of a protocol governing the remote modem connection.
 33. Amethod according to claim 31, wherein receiving at least one parameterof a remote modem connection comprises receiving an indication of a datarate of the remote modem connection.
 34. A method according to claim 31,comprising determining, by the first gateway, whether the at least oneparameter of the remote modem connection is compatible with values ofthe one or more first response signals and wherein initiating theretrain is performed only if they are determined not to be compatible.